Phase field modelling of grain boundary premelting using obstacle potentials

We investigate the multi-order parameter phase field model of Steinbach and Pezzolla [I. Steinbach, F. Pezzolla, A generalized field method for multiphase transformations using interface fields, Physica D 134 (1999) 385-393] concerning its ability to describe grain boundary premelting. For a single order parameter situation solid-melt interfaces are always attractive, which allows to have (unstable) equilibrium solid-melt-solid coexistence above the bulk melting point. The temperature dependent melt layer thickness and the disjoining potential, which describe the interface interaction, are affected by the choice of the thermal coupling function and the measure to define the amount of the liquid phase. Due to the strictly finite interface thickness also the interaction range is finite. For a multi-order parameter model we find either purely attractive or purely repulsive finite-ranged interactions. The premelting transition is then directly linked to the ratio of the grain boundary and solid-melt interfacial energy.Comment: 12 page

Studying Policy Design Quality in Comparative Perspective

This article is a first attempt to systematically examine policy design and its influence on policyeffectiveness in a comparative perspective. We begin by providing a novel concept and measure ofpolicy design. Our Average Instrument Diversity (AID) index captures whether governments tendto reuse the same policy instruments and instrument combinations or produce policy solutions that arecarefully tailored to the policy problem at hand. Second, we demonstrate that our AID index is a valid andreliable measure of policy design quality with a strong explanatory power for the outcome variables tested.Analyzing the composition of environmental policy portfolios in 21OECDcountries, we show that higherlevels of AID are positively associated with a country’s policy effectiveness in environmental matters.Based on this finding, we analyze, in a third step, the factors that lead countries to adopt more or lessdiverse policy portfolios. We find that the policy design quality is significantly improved when policymakers are not bound b

Studying Policy Design Quality in Comparative Perspective

This article is a first attempt to systematically examine policy design and its influence on policyeffectiveness in a comparative perspective. We begin by providing a novel concept and measure ofpolicy design. Our Average Instrument Diversity (AID) index captures whether governments tendto reuse the same policy instruments and instrument combinations or produce policy solutions that arecarefully tailored to the policy problem at hand. Second, we demonstrate that our AID index is a valid andreliable measure of policy design quality with a strong explanatory power for the outcome variables tested.Analyzing the composition of environmental policy portfolios in 21OECDcountries, we show that higherlevels of AID are positively associated with a country’s policy effectiveness in environmental matters.Based on this finding, we analyze, in a third step, the factors that lead countries to adopt more or lessdiverse policy portfolios. We find that the policy design quality is significantly improved when policymakers are not bound b

Viscous coalescence of droplets: a Lattice Boltzmann study

The coalescence of two resting liquid droplets in a saturated vapor phase is investigated by Lattice Boltzmann simulations in two and three dimensions. We find that, in the viscous regime, the bridge radius obeys a t^{1/2}-scaling law in time with the characteristic time scale given by the viscous time. Our results differ significantly from the predictions of existing analytical theories of viscous coalescence as well as from experimental observations. While the underlying reason for these deviations is presently unknown, a simple scaling argument is given that describes our results well.Comment: 12 pages, 10 figures; as published in Phys. Fluid

About ecology around industrial areas of Мariupol

Содержание кислорода в атмосферном воздухе городов, а также в жилых, офисных и производственных помещениях является важнейшим фактором самочувствия и здоровья горожан. При высокой температуре и высокой абсолютной влажности приземного воздуха, содержание кислорода в атмосферном воздухе минимально, и люди могут испытывать признаки гипоксии. В промышленных южных городах, к которым относится г. Мариуполь (Украина), существуют дополнительные факторы, затрудняющие дыхание человека: более высокая (относительно окружающей город территории) температура воздуха и загрязненность атмосферы, в т. ч. угарным газом и взвешенными частицами. Это приводит в условиях аномальной жары и промышленных выбросов к повышению заболеваемости и смертности городского населения. Точные измерения парциального давления и парциальной плотности кислорода требуют специального оборудования и методик, поскольку процентное содержание кислорода в атмосферном воздухе достаточно велико, а его изменения относительно малы. Большинство современных приборов, используемых городскими службами мониторинга атмосферы, ориентированы на измерение существенных отклонений содержания кислорода от нормы. Службы мониторинга состава воздуха обычно не измеряют плотность кислорода, по-видимому, из-за неявного предположения ничтожного влияния изменения метеоусловий на его содержание. Кроме того, измерение малых изменений содержания кислорода в приземном слое воздуха является достаточно сложной технической задачей. В работе представлена попытка аналитического определения распределения концентраций кислорода в приземных слоях атмосферы вокруг мест стока кислорода из атмосферы на металлургических предприятиях г. Мариуполя, приведена аналитическая модель стока кислорода из приземного слоя на основе теории «обратной струи» в одномерной постановке. Получены соответствующие изолинии концентраций на различных расстояниях от мест стока кислорода. При этом концентрация кислорода снижается обратно пропорционально расстоянию от стока, что позволяет достаточно просто оценивать распределение концентраций в приземном слое атмосферы вокруг металлургических предприятий при известных координатах мест его стока в безветренную погоду. Проанализирована пространственная изменчивость и эпизоды аномального содержания кислорода в приземном воздухе в контексте их возможного влияния на самочувствие людей.The oxygen content in the atmospheric air of cities, as well as in residential, office and industrial premises is the most important factor in the health and well-being of citizens. With high temperature and high absolute humidity of the surface air, the oxygen content in ambient air is minimal, and people may experience signs of hypoxia. In the industrial southern cities to which the city of Mariupol (Ukraine) belongs, there are additional factors that impede human breathing: higher (relative to the territory surrounding the city) air temperature and pollution of the atmosphere, including carbon monoxide and suspended particles. This results in conditions of abnormal heat and industrial emissions to an increase in the morbidity and mortality of the urban population. Accurate measurements of partial pressure and partial density of oxygen require special equipment and techniques, since the percentage of oxygen in ambient air is large enough, and its changes are relatively small. Most modern instruments used by urban atmospheric monitoring services are focused on measuring significant deviations of oxygen content from the norm. Air quality monitoring services do not usually measure the density of oxygen, apparently due to the implicit assumption of the negligible effect of changes in weather conditions on its content. In addition, the measurement of small changes in the oxygen content in the surface air is a rather complicated technical task. The paper presents an attempt to analytically determine the distribution of oxygen concentrations in the surface layers of the atmosphere around the places of oxygen runoff from the atmosphere at metallurgical enterprises of Mariupol, provides an analytical model based on the theory of "reverse flow" in a one-dimensional formulation of oxygen flow from the surface layer. The corresponding concentration contour lines were obtained at various distances from the oxygen sink sites. At the same time, the oxygen concentration decreases inversely with the distance from the drain, which makes it quite easy to estimate the distribution of concentrations in the surface layer of the atmosphere around the metallurgical enterprises at known coordinates of its drain points in calm weather. The spatial variability and episodes of anomalous oxygen content in the surface air are analyzed in the context of their possible effect on people's well-being

Relationship between solidification microstructure and hot cracking susceptibility for continuous casting of low-carbon and high-strength low-alloyed steels: A phase-field study

© The Minerals, Metals & Materials Society and ASM International 2013Hot cracking is one of the major defects in continuous casting of steels, frequently limiting the productivity. To understand the factors leading to this defect, microstructure formation is simulated for a low-carbon and two high-strength low-alloyed steels. 2D simulation of the initial stage of solidification is performed in a moving slice of the slab using proprietary multiphase-field software and taking into account all elements which are expected to have a relevant effect on the mechanical properties and structure formation during solidification. To account for the correct thermodynamic and kinetic properties of the multicomponent alloy grades, the simulation software is online coupled to commercial thermodynamic and mobility databases. A moving-frame boundary condition allows traveling through the entire solidification history starting from the slab surface, and tracking the morphology changes during growth of the shell. From the simulation results, significant microstructure differences between the steel grades are quantitatively evaluated and correlated with their hot cracking behavior according to the Rappaz-Drezet-Gremaud (RDG) hot cracking criterion. The possible role of the microalloying elements in hot cracking, in particular of traces of Ti, is analyzed. With the assumption that TiN precipitates trigger coalescence of the primary dendrites, quantitative evaluation of the critical strain rates leads to a full agreement with the observed hot cracking behavior. © 2013 The Minerals, Metals & Materials Society and ASM International

Roughness gradient induced spontaneous motion of droplets on hydrophobic surfaces: A lattice Boltzmann study

The effect of a step wise change in the pillar density on the dynamics of droplets is investigated via three-dimensional lattice Boltzmann simulations. For the same pillar density gradient but different pillar arrangements, both motion over the gradient zone as well as complete arrest are observed. In the moving case, the droplet velocity scales approximately linearly with the texture gradient. A simple model is provided reproducing the observed linear behavior. The model also predicts a linear dependence of droplet velocity on surface tension. This prediction is clearly confirmed via our computer simulations for a wide range of surface tensions.Comment: 6 pages, 8 figure

Equiaxed Dendritic Solidification Experiment (EDSE)

The objective of the research is to quantitatively determine and understand the fundamental mechanisms that control the microstructural evolution during solidification of an assemblage of equiaxed dendritic crystals. A microgravity experiment will be conducted to obtain benchmark data on the transient growth and interaction of up to four equiaxed crystals of a pure and transparent metal analog (succinonitrile, SCN) under strictly diffusion dominated conditions. Of interest in the experiment are the transient evolution of the primary and secondary dendrite tip speeds, the dendrite morphology (i.e., tip radii, branch spacings, etc.) and solid fraction, the tip selection criterion, and the temperature field in the melt for a range of initial supercoolings and, thus, interaction "strengths" between the crystals. The experiment thus extends the microgravity measurements of Glicksman and coworkers for steady growth of a single dendrite [Isothermal Dendritic Growth Experiment (IDGE), first flown on USMP-2] to a case where growth transients are introduced due to thermal interactions between neighboring dendrites - a situation more close to actual casting conditions. Corresponding earth-based experiments will be conducted to ascertain the influence of melt convection. The experiments are supported by a variety of analytical models and numerical simulations. The data will primarily be used to develop and test theories of transient dendritic growth and the solidification of multiple interacting equiaxed crystals in a supercooled melt