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A modified cellular automaton model (MCA) was developed in order to simulate the evolution of dendritic microstructures in solidification of alloys. Different from the classical cellular automata in which only the temperature field was calculated, this model also included the solute redistribution both in liquid and solid during solidification. The finite volume method, which was coupled with the cellular automaton model, was used to calculate the temperature and solute fields in the domain. The relationship between the growth velocity of a dendrite tip and the local undercooling was calculated according to the KGT (Kurz-GiovanolaTrivedi) model. The effects of constitutional undercooling and curvature undercooling on the equilibrium interface temperature were also considered in the present model. The MCA model was applied to predict the dendritic microstructures, such as the free dendritic growth from an undercooled melt and competitive dendritic growth in practical casting solidification. The simulated results were compared with those obtained experimentally.

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A modified cellular automaton (MCA) coupled with a momentum and species transport model has been developed in order to predict the evolution of dendritic morphology during solidification of alloys in the presence of melt convection. In the present model, the cellular automaton algorithm for dendritic growth is incorporated with the transport model, for calculating fluid flow and mass transfer by both convention and diffusion. The MCA model takes into account the effects of the constitutional undercooling and the curvature undercooling on the equilibrium interface temperature. It also considers the preferred growth orientation of crystals and solute redistribution during solidification. In the transport model, which is coupled with cellular automaton approach, the SIMPLE scheme is employed to solve the governing equations of momentum and species transfers. The present model was applied to model solutal dendritic growth of an Al-3mass%Cu alloy in a forced flow. The simulations reproduced the typical asymmetric growth features of convective dendrites with various preferred orientations. The effects of inlet flow velocity on the solute redistribution and the growth velocity of a dendritic tip were quantitatively investigated.

Droplet nucleation and growth on superhydrophobic nanoarrays is simulated by employing a multiphase, multicomponent lattice Boltzmann (LB) model. Three typical preferential nucleation modes of condensate droplets are observed through LB simulations with various geometrical parameters of nanoarrays, which are found to influence the wetting properties of nanostructured surfaces significantly. The droplets nucleated at the top of posts (top nucleation) or in the upside interpost space of nanoarrays (side nucleation) will generate a nonwetting Cassie state, while the ones nucleated at the bottom corners between the posts of nanoarrays (bottom nucleation) produce a wetting Wenzel state. The simulated time evolutions of droplet pressures at different locations are analyzed, which offers insight into the underlying physics governing the motion of droplets growing from different nucleation modes. It is demonstrated that the nanostructures with taller posts and a high ratio of post height to interpost space (H/S) are beneficial to produce the top- and side-nucleation modes. The simulated wetting states of condensate droplets on the nanostructures, having various geometrical configurations, compare reasonably well with experimental observations. The established relationship between the geometrical parameters of nanoarrays and the preferential nucleation modes of condensate droplets provides guidance for the design of nanoarrays with desirable anticondensation superhydrophobic properties.

The evolution of globular and dendritic structures in solidification of an Al-7mass%Si alloy has been investigated by a modified cellular automaton model (MCA). Besides retaining the probabilistic aspects of the classical CA model for the heterogeneous nucleation and the preferential growth orientations of the nuclei, the present MCA model is coupled with the curvature, the solute partition between liquid and solid as well as diffusion in both phases. The effects of constitutional undercooling and curvature undercooling are incorporated on the equilibrium interface temperature. The relationship between the growth velocity of a dendrite tip and the local undercooling is calculated according to the KGT (Kurz-Giovanola-Trivedi) model. The finite volume method, coupled with the cellular automaton model, was used to calculate the solute field in the computational domain. The effects of pouring temperature, cooling rate, and inoculation on the growth morphology of the primary phase were studied. The simulation results were compared with those obtained experimentally. It can be concluded that the present simulation model can successfully predict the evolution of dendritic and globular structures in solidification of alloys.KEY WORDS: solidification microstructure; modified cellular automaton; nucleation; growth kinetics; solute redistribution; diffusion; curvature; semi-solid casting; globular structure; dendrite structure.formation of dendritic structures in solidification of alloys.14)The purpose of the present study is to study the morphology evolution of the primary phase, i.e., dendritic, intermediate rosette-like and globular, in solidification of Al-7mass%Si alloy using a modified cellular automaton (MCA) model. The effects of pouring temperature, cooling rate and inoculation on the morphology of the primary phase were examined. The simulated results were compared with those obtained experimentally. Experimental ProcedureAn Al-7.0mass%Si alloy was prepared using commercial pure aluminum (99.9%) and metallic silicon in an electrical resistance furnace. The inoculation was achieved by the addition of Al-5Ti-B master alloy to the level of 0.01 mass% Ti. The melt temperature was initially kept at 700°C for a specified period, and then slowly cooled down to various temperatures in a crucible. Subsequently, the melt was poured into a preheated steel mold having a thermally insulated bottom placed in a temperature holding furnace in order to cool the specimen with various cooling rates. The experimental apparatus is shown in Fig. 1. A thermocouple was positioned in the center of the mold cavity to measure the cooling curves of the slurry. The temperature-time curve of the slurry was recorded using a data-acquisition unit. The slurry specimen was quenched into water when it was cooled down to a specified temperature. The specimens for metallographic observation were cut from the area near to the thermocouple, polished and then etched with Tucker solution. Mathematical Formulation and Numerical Method Model DescriptionTh...

We developed a novel graphene-modified carbon fiber microelectrode (GCFME) to determine dopamine in mice hippocampus tissue. The electrochemical behavior of GCFME is characterized by potassium ferricyanide, dopamine (DA), ascorbic acid (AA) and uric acid (UA) by cyclic voltammetry (CV). Graphene makes a favorable electron transfer process for the oxidation of DA, AA, UA, and provides well-resolved oxidative peaks of the three. The microsensor for DA shows good sensitivity and selectivity, with a linear range from 1.0 10 À8 M to 1.0 10 À4 M and a detection limit of 1.0 10 À8 M. This graphene-based microelectrode successfully monitored the release of dopamine in vitro.