Consequence Of Coalescence Research Articles

An archetype for evolving dynamics of primitive human culture

From the very beginning, human civilizations have evolved and spread across the surface of the planet Earth through various dynamical processes such as growth, assimilation, invasion, aggression, and annihilation. Such processes being responsible for expansion, integration, destruction, and reconstruction of civilizations, used to play key roles in the tides of time and fabric today’s multicultural societies. A culture, being an inherent entity of human civilization, also evolves in conformity with civilizations. As such, the evolution of cultures can be understood as an artifact of such dynamical processes. How such dynamical processes initiate the diversification of cultures from small-scale simple societies? Why most of the cultures go extinct and why some survive for a comparatively longer period even after facing several wars and attacks? What plays a key role in creating a multicultural society? In order to partially answer all such highly stimulating questions, here we are interested in tackling the problem by giving importance to the nature of governing dynamical processes. Hence we perform a set of computer simulations on an archetypal model where a large number of independent and isolated primitive human cultures, being distributed randomly in a two-dimensional domain, are allowed to evolve following some historically-inspired rules for expansion, interaction, and merging processes among the cultures. As they evolve through inter-cultural interactions, the surviving cultures dynamically inherit the characteristics of their ancestors, leading to a well-mixed globally-polarise culture that emerges depending on the frequency and casualties of wars, consequences of coalescence, and similarity factors. From the ensuing simulation results, we find in accord with the historical fact that the rich diversity in a surviving culture is a consequence of all the dynamical processes that act repeatedly during its entire evolutionary track. We also visualize through our model how a global monocultural state and colonization among multicultural societies emerge separately in the modern period. We highlight a number of possible avenues for future research along these lines.

Influence of Grain Growth Inhibitors and Powder Size on the Properties of Ultrafine and Nanostructured Cemented Carbides Sintered in Hydrogen

The influence of grain growth inhibitors and powder size on the microstructure and mechanical properties of ultrafine and nanostructured cemented carbides was researched. Three different WC powders, with an addition of different type and content of grain growth inhibitors GGIs, VC and Cr3C2 and with dBET grain sizes in the range from 95 to 150 nm were selected as starting powders. Four different mixtures with 6 and 9 wt. % Co were prepared. The consolidated samples are characterized by different microstructural and mechanical properties with respect to the characteristics of starting powders. Increased sintering temperatures led to microstructural irregularities in the form of a discontinuous WC growth, carbide agglomerates and abnormal grain growth as a consequence of coalescence via grain boundary elimination. The addition of 0.45% Cr3C2 contributed to microstructure homogeneity, reduced discontinuous and continuous grain growth, and increased Vickers hardness by approximately 70 HV and fracture toughness by approximately 0.15 MN/m3/2. The reduction of the starting powder to a real nanosize of 95 nm resulted in lower densities, and significant hardness increase, with a simultaneously small increase in fracture toughness. The consolidation of real nanopowders (dBET < 100 nm) solely by conventional sintering in hydrogen without isostatic pressing is not preferred.

Features of the dynamics of the heavy bubble magma state in explosive volcanic eruptions

The explosive eruption of a volcano that occurs when a volcanic canal is suddenly depressurized is one of the mysterious phenomena of nature, the mechanism of which is associated with the sudden decompression of a high-pressure magma containing dissolved gas and microcrystallites and with its transition to a multiphase state. With the obvious lack of the possibility to directly investigate these processes, the problem of experimental and numerical modeling, and creation of mathematical models that would allow describing the state of magma during various stages of eruption with a certain degree of adequacy are becoming topical. A model combining systems of equations of the mechanics of multiphase media is proposed. The model is formulated on the basis of the modified Iordansky–Kogarko–van Wijngaarden model with the Navier-Stokes equation for the variable viscosity, and the full range of kinetic relationships, including spontaneous nucleation and saturation dynamics of magma with cavitation nuclei. An analysis of a pre-explosive state of a number of volcanoes was carried out, which showed that the structural features of explosive volcanoes are analogous to the schemes of hydrodynamic shock tubes (UT), such as Glass-Heuckroth. Experimental modeling of the flow structure demonstrates the probability of the formation of the projectile regime as a consequence of coalescence of bubbles in the flow. A physical model of combined explosive volcanic eruptions is proposed; the process of formation in the magma flux of an independent flow of crystalline clusters (magmatic ”bombs“) moving with respect to the flow of cavitating magma at a much higher rate is experimentally studied.

A Simple Computational Technique for the Systematic Study of Adsorption Effects in Emulsified Systems. Influence of Inhomogeneous Surfactant Distributions on the Coalescence Rate of a Bitumen-in-water Emulsion

In order to study the evolution of a bitumen-in-water (B/W) emulsion with time, a modification of a standard Brownian Dynamics (BD) algorithm was made. In these calculations, the 3-D movement of emulsion drops is mimicked by a combination of a steady DLVO (Derjaguin-Landau-Verwey-Oberbeek) inter-drop force and a random kick. The electrostatic component of the DLVO potential is allowed to depend on the surfactant population at the interface of each drop. Surfactant adsorption changes with the total surfactant concentration of the system, the available interfacial area, and the initial spatial distribution of amphiphilic molecules. Depending on these variables, the drops can flocculate and coalesce with either real drops or periodic-boundary images. As a consequence of coalescence, the interfacial area diminishes and surfactant is re-distributed among the surviving drops. The results are compared with well-known analytical equations developed for much simpler cases. With the present simulation technique, the exponential decrease of the number of drops with time reported for B/W systems can be reproduced. Evidence of a monotonic relationship between the total interfacial area of the surviving drops and the total surfactant concentration is also presented.

Ultrathin epitaxial iron films on a highly asymmetrical substrate: Fe/Cu(311).

The structure and morphology of ultrathin epitaxial Fe films on Cu(311) is examined in situ by spot-profile analyzing low-energy electron diffraction. Cu(311) is a highly asymmetrical substrate which is characterized by a troughlike surface structure composed of uniaxially arranged close-packed Cu atom rows. Deposition at 140 K initially leads to the formation of pseudomorphic Fe. The constraint to lower dominant stress along the close-packed atom rows forces the formation of pseudomorphic patches with a quasiperiodic separation of 35 \AA{}. With proceeding growth, these patches act as nucleation sites for three-dimensional islands that gradually relax via a Pitsch transformation towards a strained bcc structure. Coalescence occurs at \ensuremath{\sim}5 ML and leads to a periodically faceted growth front of the overlayer. The resulting surface topography corresponds to a regular up-and-down staircase and remains unchanged for coverages g5 ML: the periodic facet separation measures 35 \AA{}; 7--8 layers contribute to the growth front. As a consequence of coalescence, the film locks into a lattice arrangement which is predominantly dictated by the substrate and is likely to correspond to an fcc-like structure. The periodic facetting of the film surface, on the other hand, allows partial relaxation towards strained bcc structure to persist in the top layers of the film. \textcopyright{} 1996 The American Physical Society.

The nucleus in solid state reactions: Towards a definition

The term nucleus, as applied to solid state reactions, defines a product aggregate capable of sustained and unrestricted growth by continual acquisition of material at a chemically active periphery that constitutes the reactant/product interface. Such an interface is any laminar boundary contact zone, at the surface of a nucleus, within which chemical changes and/or phase transformations preferentially occur. Nucleation, the initial establishment of a new and discrete particle of product (nucleus) within the solid reactant, is usually identified as the crystallographic transformation or structural reorganization that generates the smallest possible quantity of the product phase. Nucleation sites are the limited number of sub-microscopic domains within the reactants at which nucleation most readily occurs: these are structures of locally enhanced reactivity and usually identified as crystal imperfections at surfaces (damage, impurity, etc.). Precursor reactions, preceding the establishment of a nucleus, may yield product that is initially capable of retaining structural features of the reactant (topotaxy). Each individual assemblage, possessing enhanced reactivity but not yet transformed into product, may be termed an incipient nucleus. Nucleation is identified as the subsequent transformation by which this initial accumulation of reacted material is organized or recrystallized into the structure characteristic of the product phase(s): this product particle is the germ nucleus. Interfacial free energy properties of these very small germ nuclei are believed to reduce their reactivity so that their rates of initial development may be relatively slower than that subsequently achieved when these become the larger developing assemblages, the growth nuclei. A growth nucleus, often simply referred to as a nucleus, is the aggregate total assemblage of product or recrystallized material that accumulated following a single nucleation event. We believe that communication in the subject would be clarified if the term nucleus was always used with a descriptive adjective, examples being: nucleation site, incipient nucleus, germ nucleus, growth nucleus, nucleus interface. The nomenclature is intended to be equally applicable to reactions involving a single solid, and to reactions of a solid with another reactant, gas, liquid or solid. Product formation occurs within the active interface of reactant-product contact that defines the nucleus periphery. This interface advances through unchanged reactant, usually without restriction, and is expected to propagate to all reactant crystal edges, or its progression may be locally terminated as a consequence of coalescence with a neighbouring growth nucleus. Interface movement may proceed at different rates in different crystallographic directions and may be subject to diffusion control, of reactants to the interface or products away, as nucleus growth continues. The product assemblages that constitute a single nucleus may remain coherent or the product particles may become progressively dispersed as the nucleus grows. Interfacial strain accompanying growth may sometimes result in product detachment or even crystallite disintegration.