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We develop a ReaxFF reactive force field used for the molecular dynamics simulations of thermophysical properties of liquid Cu and Zr metals. The ReaxFF parameters are optimized by fitting to the first-principles density-functional calculations on the equations of state for bulk crystal structures and surface energies. To validate the force field, we compare the ReaxFF results with those from experiments and embedded-atom-method (EAM) potentials. We demonstrate that the present ReaxFF force field well represents structural characteristics and diffusion behaviors of elemental Cu and Zr up to high-temperature liquid regions. It reasonably reproduces the thermodynamic processes associated with crystal-liquid interface. In particular, the equilibrium melting temperatures show better agreement with experimental measurements than the results from EAM potentials. The ReaxFF reactive force field method exhibits a good transferability to the nonreactive processes of liquid systems. [ABSTRACT FROM AUTHOR]

Liquids attain a metastable state without crystallizing by cooling rapidly to a given temperature below the melting point. With increasing supercooling, the nucleation rate would show an increase based on the prediction of the classical nucleation theory. It is generally thought that the nucleation rate will reach the maximum upon approaching the glass transition temperature, Tg, for glass-forming liquids. We report that there exists a supercooled region above Tg in which the crystallization has actually been severely suppressed. Our molecular dynamics simulations show that the growth of embryos in the supercooled Cu60Zr40 melt is subjected to a strong anisotropic stress associated with the dynamic heterogeneity. Its long-range effect drives the embryo to grow into a ramified morphology so that the interface energy dominates over the embryo growth, leading to the suppression of nucleation. [ABSTRACT FROM AUTHOR]

Crystal growth of the glass-forming CuZr alloy is shown to be abnormally slow, which suggests a new method to identify the good glass-forming alloys. The crystal growth of elemental Cu, Pd and binary NiAl, CuZr alloys is systematically studied with the aid of molecular dynamics simulations. The temperature dependence of the growth velocity indicates the different growth mechanisms between the elemental and the alloy systems. The high-speed growth featuring the elemental metals is dominated by the non-activated collision between liquid-like atoms and interface, and the low-speed growth for NiAl and CuZr is determined by the diffusion across the interface. We find that, in contrast to Cu, Pd, and NiAl, a strong stress layering arisen from the density and the local order layering forms in front of the liquid-crystal interface of CuZr alloy, which causes a slow diffusion zone. The formation of the slow diffusion zone suppresses the interface moving, resulting in much small growth velocity of CuZr alloy. We provide a direct evidence of this explanation by applying the compressive stress normal to the interface. The compression is shown to boost the stress layering in CuZr significantly, correspondingly enhancing the slow diffusion zone, and eventually slowing down the crystal growth of CuZr alloy immediately. In contrast, the growth of Cu, Pd, and NiAl is increased by the compression because the low diffusion zones in them are never well developed. [ABSTRACT FROM AUTHOR]

It is previously predicted that the equilibrium shape of a rotating liquid drop evolves from the axisymmetric to the two-, three-, and four-lobed morphologies as the angular velocity increases. Although the two- and three-lobed shape bifurcations have been observed in experiments, the four-lobed equilibrium shape is scarcely reported. Here, we investigate the multiple-lobed shape bifurcations of rotating drops by using acoustic levitation, and in particular, follow the evolution of the four-lobed equilibrium shape. A new shape family of rotating drops characterized by five-lobed bifurcation is also observed, which is unexpected in the theoretical predictions. A numerical method is employed to simulate the shape evolution of acoustically levitated and rotating drops. And the results validate the existence of bifurcation point shifts among all the lobed-shape families due to the initial drop flattening induced by the acoustic radiation pressure, which plays a decisive role in the emergence of the five-lobed shape. [ABSTRACT FROM AUTHOR]

The interdiffusion processes in liquid Al–Cu and Ni–Cu alloys are studied by using molecular dynamics simulation method. The Maxwell–Stefan (MS) diffusivities are calculated over a wide composition range with both the Green–Kubo method and the Darken relation. Comparisons show that the Darken relation predicts well the MS diffusivity for Ni–Cu alloy, while overestimates the value for Al–Cu alloy, especially in the medium concentration region. Based on the calculated MS diffusivities and the activities of the alloys, the Fickian interdiffusivities are predicted. The results show strong dependences on the compositions of the alloys. In addition, the Fickian interdiffusivities of Al60Cu40 and Ni50Cu50 melts as a function of undercooling are estimated, which is proved to be beneficial in improving the quantitative predictions of dendrite growth velocity in solidification. [ABSTRACT FROM AUTHOR]

The supercooling capability of aqueous NaCl and KCl solutions is investigated at containerless state by using acoustic levitation method. The supercooling of water is obviously enhanced by the alkali metal ions and increases linearly with the augmentation of concentrations. Furthermore, the supercooling depends on the nature of ions and is 2–3 K larger for NaCl solution than that for KCl solution in the present concentration range: Molecular dynamics simulations are performed to reveal the intrinsic correlation between supercoolability and microstructure. The translational and orientational order parameters are applied to quantitatively demonstrate the effect of ionic concentration on the hydrogen-bond network and ice melting point. The disrupted hydrogen-bond structure determines essentially the concentration dependence of supercooling. On the other hand, the introduced acoustic pressure suppresses the increase of supercooling by promoting the growth and coalescence of microbubbles, the effective nucleation catalysts, in water. However, the dissolved ions can weaken this effect, and moreover the degree varies with the ion type. This results in the different supercoolability for NaCl and KCl solutions under the acoustic levitation conditions. [ABSTRACT FROM AUTHOR]

Objective: To verify the reliability and feasibility of Hoffmann method in establishing pediatric reference intervals (RI) of erythrocyte count., Methods: Three hundreds and ninty-two thousands of hospital-based data for erythrocyte count of children aged in 1 to 17, measured by the Sysmex Xs-800i, was collected from Beijing Children's Hospital during January to December 2014. Outliers were removed using the Dixon method, then Hoffmann method was conducted to establish the gender and age stratified pediatric RIs of erythrocyte count. The erythrocyte count of 2 217 healthy children, recruited from Beijing Children's Hospital and Liaocheng Children's Hospital in Shandong province, was conducted as normal reference to verify the reliability of Hoffmann method in establishing RIs and to compare with existing RIs., Results: In 4 subgroups as following, male aging 1 to 12 years, male aging 13 to 17 years, female aging 1 to 12 years, female aging 13 to 17 years, the RIs of erythrocyte count established using Hoffmann method were (4.1-5.4)×10(12)/L, (4.4-5.7)×10(12)/L, (4.0-5.3)×10(12)/L, (4.0-5.3)×10(12)/L, respectively. The verification results in 2 217 healthy children showed that the proportions of out of range in four subgroups were 6.17%, 8.81%, 6.22%, 7.78%, respectively., Conclusion: Hoffmann method produce reliable RIs according with the actual situation in healthy children, which is also convenient and is worth popularizing in clinical practice.