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Self-organization that leads to the discontinuous emergence of optimized new patterns is related to entropy generation and the export of entropy. Compared to the original pattern that the new, self-organized pattern replaces, the new features could involve an abrupt change in the pattern-volume. There is no clear principle of pathway selection for self-organization that is known for triggering a particular new self-organization pattern. The new pattern displays different types of boundary-defects necessary for stabilizing the new order. Boundary-defects can contain high entropy regions of concentrated chemical species. On the other hand, the reorganization (or refinement) of an established pattern is a more kinetically tractable process, where the entropy generation rate varies continuously with the imposed variables that enable and sustain the pattern features. The maximum entropy production rate (MEPR) principle is one possibility that may have predictive capability for self-organization. The scale of shapes that form or evolve during self-organization and reorganization are influenced by the export of specific defects from the control volume of study. The control volume (CV) approach must include the texture patterns to be located inside the CV for the MEPR analysis to be applicable. These hypotheses were examined for patterns that are well-characterized for solidification and wear processes. We tested the governing equations for bifurcations (the onset of new patterns) and for reorganization (the fine tuning of existing patterns) with published experimental data, across the range of solidification morphologies and nonequilibrium phases, for metallic glass and featureless crystalline solids. The self-assembling features of surface-texture patterns for friction and wear conditions were also modeled with the entropy generation (MEPR) principle, including defect production (wear debris). We found that surface texture and entropy generation in the control volume could be predictive for self-organization. The main results of this study provide support to the hypothesis that self-organized patterns are a consequence of the maximum entropy production rate per volume principle. Patterns at any scale optimize a certain outcome and have utility. We discuss some similarities between the self-organization behavior of both inanimate and living systems, with ideas regarding the optimizing features of self-organized pattern features that impact functionality, beauty, and consciousness.
Jainagesh A. Sekhar. Self-Organization, Entropy Generation Rate, and Boundary Defects: A Control Volume Approach. Entropy 2021, 23, 1092 .
AMA StyleJainagesh A. Sekhar. Self-Organization, Entropy Generation Rate, and Boundary Defects: A Control Volume Approach. Entropy. 2021; 23 (8):1092.
Chicago/Turabian StyleJainagesh A. Sekhar. 2021. "Self-Organization, Entropy Generation Rate, and Boundary Defects: A Control Volume Approach." Entropy 23, no. 8: 1092.
The melt pool dimensions and pool-shapes that are possible with directed beam-heating are explored with a collapsed parameter model, and compared with experimental results. The peak temperatures, temperature gradients and fluid flow velocities/cells are calculated for various beam parameters. The key solidification parameters including the interface velocity are discussed for various beam powers, beam size and interaction times. The new Maximum Entropy Production Rate (MEPR) solidification theory and its successful predictions are reviewed. The ensuing prediction of the scale of the smallest feature of the microstructure is discussed.
Jainagesh Akkaraju Sekhar. Rapid solidification and surface topography for additive manufacturing with beam surface heating. Current Opinion in Chemical Engineering 2020, 28, 10 -20.
AMA StyleJainagesh Akkaraju Sekhar. Rapid solidification and surface topography for additive manufacturing with beam surface heating. Current Opinion in Chemical Engineering. 2020; 28 ():10-20.
Chicago/Turabian StyleJainagesh Akkaraju Sekhar. 2020. "Rapid solidification and surface topography for additive manufacturing with beam surface heating." Current Opinion in Chemical Engineering 28, no. : 10-20.
The use of the principle of maximum entropy generation per unit volume is a new approach in materials science that has implications for understanding the morphological evolution during solid–liquid interface growth, including bifurcations with or without diffuseness. A review based on a pre-publication arXiv preprint is first presented. A detailed comparison with experimental observations indicates that the Maximum Entropy Production Rate-density model (MEPR) can correctly predict bifurcations for dilute alloys during solidification. The model predicts a critical diffuseness of the interface at which a plane-front or any other form of diffuse interface will become unstable. A further confidence test for the model is offered in this article by comparing the predicted liquid diffusion coefficients to those obtained experimentally. A comparison of the experimentally determined solute diffusion constant in dilute binary Pb–Sn alloys with those predicted by the various solidification instability models (1953–2011) is additionally discussed. A good predictability is noted for the MEPR model when the interface diffuseness is small. In comparison, the more traditional interface break-down models have low predictiveness.
Yaw Delali Bensah; J. A. Sekhar. Solidification Morphology and Bifurcation Predictions with the Maximum Entropy Production Rate Model. Entropy 2019, 22, 40 .
AMA StyleYaw Delali Bensah, J. A. Sekhar. Solidification Morphology and Bifurcation Predictions with the Maximum Entropy Production Rate Model. Entropy. 2019; 22 (1):40.
Chicago/Turabian StyleYaw Delali Bensah; J. A. Sekhar. 2019. "Solidification Morphology and Bifurcation Predictions with the Maximum Entropy Production Rate Model." Entropy 22, no. 1: 40.
Life-cycle studies provide a comprehensive insight into comparative innovation behavior and innovation constants. In this article a comparison of the life-cycle plots for the production and patent activity is made for US energy production categories. As has been shown previously for material production [TFSC, vol.78, 2011], the two activities may be correlated to such an extent that they may be superimposed to a large degree, for all growth stage except stage IV, simply by an origin-shift. Over ten energy production methods have been studied in this manner for the first time. An origin-shift ratio, OR, (positive or negative lag) describes the amount required to shift the two activity curves in order to superimpose them. The relative drive-force ratio, DR (defined as the ratio of the production and patent growth constants) is noted to scale with the origin-shift. The value of this drive-force ratio determines the amount of production that is influenced by patents. The slope of curve of the drive-force ratio plotted against the origin-shift ratio is noted to be constant across all energy categories in the high growth Stage III. The authors find for the first time that even early stage production displays an origin-shift. Energy materials (i.e., those materials that dominate a particular type of energy production) are also studied in the material category alone, where the total usage of the material is considered. The concept of Green materials is discussed in this context. The life-cycle approach collapses the energy categories/sources and related materials into two groups. The authors discuss these groups in the Schumpeterian framework of constructive and destructive innovation. Group 1, containing coal, natural gas, wind, renewable, fossil fuel, solar and total energies, is composed of energy categories/sources whose patent activity could be inferred as driving their production. On the other hand, energy production from biomass, biofuel, geothermal and nuclear energies is identified in Group 2, in which the patent activity is driven by production (high innovation group). An (OR) of slightly less than one and a (DR) less than one, lead to a placement where with time, a constructive to destructive innovation transition is encountered A very low (OR) and a low (DR) on the other hand leads to a transition from Stage III growth to a no-growth (Stage IV) with time. Innovation enhanced resources and production are also discussed.
Michael C. Connelly; J.A. Sekhar. U. S. energy production activity and innovation. Technological Forecasting and Social Change 2012, 79, 30 -46.
AMA StyleMichael C. Connelly, J.A. Sekhar. U. S. energy production activity and innovation. Technological Forecasting and Social Change. 2012; 79 (1):30-46.
Chicago/Turabian StyleMichael C. Connelly; J.A. Sekhar. 2012. "U. S. energy production activity and innovation." Technological Forecasting and Social Change 79, no. 1: 30-46.
This chapter contains sections titled: Introduction Banded Structures in NiAl Brusselator Model for NiAl X‐Ray Analysis Thermal Profile Analysis Nano‐Particles and Nano‐Bands Processing Routes for Kinetic Manipulation Conclusions
H.P. Li; G.K. Dey; J.A. Sekhar. New Entropic Routes for Nano-Bands and Nano-Particles. Processing of High Temperature Superconductors 2011, 21 -34.
AMA StyleH.P. Li, G.K. Dey, J.A. Sekhar. New Entropic Routes for Nano-Bands and Nano-Particles. Processing of High Temperature Superconductors. 2011; ():21-34.
Chicago/Turabian StyleH.P. Li; G.K. Dey; J.A. Sekhar. 2011. "New Entropic Routes for Nano-Bands and Nano-Particles." Processing of High Temperature Superconductors , no. : 21-34.
The maximum entropy production rate (MEPR) in the solid–liquid zone is developed and tested as a possible postulate for predicting the stable morphology for the special case of steady state directional solidification (DS). The principle of MEPR states that, if there are sufficient degrees of freedom within a system, it will adopt a stable state at which the entropy generation (production) rate is maximized. Where feasible, the system will also try and adopt a steady state. The MEPR postulate determines the most probable state and therefore allows pathway selections to occur in an open thermodynamic system. In the context of steady state solidification, pathway selections are reflected in the corresponding morphological selections made by the system in the solid–liquid (mushy) zone in order to cope with the required entropy production. Steady state solidification is feasible at both close to, and far from equilibrium conditions. Based on MEPR, a model is proposed for examining the stability of various morphologies that have been experimentally observed during steady state directional solidification. This model employs a control volume approach for entropy balance, including the entropy generation term (S gen), which depends on the diffuse zone and average temperature of the solid–liquid region within the control volume. In this manner, the model takes a different approach from the successful kinetic models that have been able to predict key features of stable morphological patterns. Unstable planar interfaces, faceted cellular arrays, cell–dendrite transitions, half cells both faceted and smooth, and other transitions such as the absolute stability transition at high solid/liquid velocities are examined with the model. Uncommon solidification morphological features such as non-crystallographic dendrites and discontinuous cell-tip splitting are also examined with the model. The preferred morphological change-direction for the emergence of the stable morphological feature is inferred with the MEPR postulate in a manner analogous to the free energy minimization principle(s) when used for predicting phase stability and metastable phase formation. Aspects of mixed-mode order transformation characteristics are also discussed for non-equilibrium solidification containing a diffuse interface, in contrast to classifying solidification as purely a first order transformation. The MEPR model predictions are shown to follow the experimental transitions observed to date in several historical studies.
J. A. Sekhar. The description of morphologically stable regimes for steady state solidification based on the maximum entropy production rate postulate. Journal of Materials Science 2011, 46, 6172 -6190.
AMA StyleJ. A. Sekhar. The description of morphologically stable regimes for steady state solidification based on the maximum entropy production rate postulate. Journal of Materials Science. 2011; 46 (19):6172-6190.
Chicago/Turabian StyleJ. A. Sekhar. 2011. "The description of morphologically stable regimes for steady state solidification based on the maximum entropy production rate postulate." Journal of Materials Science 46, no. 19: 6172-6190.
A relationship is inferred between dissipative reactions, nanocrystal formation and nanobands in micropyretically synthesized equimolar Ni–Al alloys. Various microkinetic mechanisms may be operative, depending on the chosen processing conditions and alloy chemistry. Time-lapse X-ray reports, microstructural studies, process conditions and combustion calculations are correlated to understand the microkinetics of the synthesis process. Dissipative oscillatory chemical reactions, called Belousov–Zhabotinsky (BZ) reactions, are proposed as one synthesis mechanism, which leads to the formation of the observed nanoscale features such as nanoparticles and nanobands. Nanoband features in a solid-state combustion processes are discussed for the first time. The dissipative oscillations that are a consequence of the nonlinear reaction rate equations create and simultaneously disperse nanoparticles and nanobands depending on the initial temperature, composition and other process conditions chosen. The spatiotemporal structure from a moving geometrical configuration such as a micropyretic solid-state combustion front can contain a decaying dissipative reaction product, e.g. a spin combustion microstructure. Nanoband-forming waves and nanocrystals possibly interact, leading to unique variations in the structure. Such nanostructural possibilities could be advantageously controlled by manipulating the initial conditions. The implications of the BZ finding could be significant, as it offers a method of forming bulk near-net-shaped objects containing nanostructured enhancements. For the NiAl material in particular, this could be a significant technical advantage from a manufacturing viewpoint. Some possible methods to influence the process and the resultant structure on the nanoscale are discussed.
J.A. Sekhar; H.P. Li; G.K. Dey. Decay-dissipative Belousov–Zhabotinsky nanobands and nanoparticles in NiAl. Acta Materialia 2010, 58, 1056 -1073.
AMA StyleJ.A. Sekhar, H.P. Li, G.K. Dey. Decay-dissipative Belousov–Zhabotinsky nanobands and nanoparticles in NiAl. Acta Materialia. 2010; 58 (3):1056-1073.
Chicago/Turabian StyleJ.A. Sekhar; H.P. Li; G.K. Dey. 2010. "Decay-dissipative Belousov–Zhabotinsky nanobands and nanoparticles in NiAl." Acta Materialia 58, no. 3: 1056-1073.
Micropyretic synthesis is an autosynthesis route which requires minimal external energy. During synthesis, a high-temperature reaction front propagates in a uniform or unstable manner depending on the conditions chosen, thereby converting a reactant mix to the desired products accompanied by a large amount of entropy production. Sometimes banded microstructural features are noted to form (frozen into the final solid), often with a fixed periodicity. This banded structure is thought to be the signature of an oscillating wave front. In previous articles by us and others, banded structures and other residual instabilities have been thought to arise from variations in the combustion front velocity caused by a mismatch between the heat diffusion rate and the heat production rate from the product synthesis (i.e. from exceeding the critical Lewis number and related bifurcations). Such oscillations have been modeled in the past by a single overall reaction formulation and corresponding heat flow solution which we refer to as the extended Merzhanov model. Spiral fronts are also recognized in the literature. We believe now that banded structures could also arise from entropy generating, dissipative, Belousov-Zhabotinsky (BZ) type reactions. Such reactions are discussed in this article. The overall BZ reaction progresses in the form of a nonlinear oscillator with several intermediary steady-state sub-reactionscontained in a reaction volume. We propose sub-reaction formulations by which a BZ reaction may occur during micropyretic synthesis. Micropyretic synthesis can display both types of oscillations, i.e. the Lewis type and the BZ type. We discuss materials systems where the BZ oscillations are possible, namely, the Ti-B and Ni-Al alloy systems. A comparison with experiments shows that the micropyretic product-chemistry is adequately predicted for the first time by a BZ formulation in both the Ti-B and several Ni-Al alloy systems. Wherever feasible compositional data reported in the literature are compared with the new predictions. It appears invoking the BZ yields a better picture of the final products.
H. P. Li; J. A. Sekhar. Recognition of Belousov-Zhabotinsky-type oscillations in autosynthetic micropyretic reactions. International Journal of Self-Propagating High-Temperature Synthesis 2009, 18, 219 -234.
AMA StyleH. P. Li, J. A. Sekhar. Recognition of Belousov-Zhabotinsky-type oscillations in autosynthetic micropyretic reactions. International Journal of Self-Propagating High-Temperature Synthesis. 2009; 18 (4):219-234.
Chicago/Turabian StyleH. P. Li; J. A. Sekhar. 2009. "Recognition of Belousov-Zhabotinsky-type oscillations in autosynthetic micropyretic reactions." International Journal of Self-Propagating High-Temperature Synthesis 18, no. 4: 219-234.
A comparison is made of die temperature uniformity for two heating configurations: electric air heating and flame heating. The temperature uniformity with electric air heating is noted to be substantially superior to flame heating of large dies. The simulation results are compared with experimentally obtained numbers and found to be in agreement.
Biswajit Basu; Santhanu Jana; G. S. Reddy; J. A. Sekhar. Simulating convective die heating for forgings and pressure casting. JOM 2002, 54, 39 -43.
AMA StyleBiswajit Basu, Santhanu Jana, G. S. Reddy, J. A. Sekhar. Simulating convective die heating for forgings and pressure casting. JOM. 2002; 54 (8):39-43.
Chicago/Turabian StyleBiswajit Basu; Santhanu Jana; G. S. Reddy; J. A. Sekhar. 2002. "Simulating convective die heating for forgings and pressure casting." JOM 54, no. 8: 39-43.