Phase-field lattice Boltzmann model for interface tracking of a binary fluid system based on the Allen-Cahn equation.

A lattice Boltzmann (LB) model is proposed to track the interface of binary fluid system based on the conservative-form Allen-Cahn (A-C) equation for phase field. Utilizing an equilibrium distribution function and a modified LB equation, this model is able to correctly recover the conservative A-C equation through the Chapman-Enskog analysis. A series of two-dimensional (2D) and three-dimensional (3D) phase-capturing benchmark tests have been conducted for validation, which include the diagonal translation of a circular interface, the rigid-body rotation of a Zalesak disk, and the deformation of 2D circular interface and 3D spherical interface in shear flows, all illustrating better accuracy and stability of the proposed model than the previous models tested. By coupling the incompressible hydrodynamic equation, a stationary droplet, a spinodal decomposition, and the Rayleigh-Taylor instability are simulated as well, showing the satisfying performance of the model in dealing with complex interfaces of binary fluid systems.

Single Droplet on Micro Square-Post Patterned Surfaces - Theoretical Model and Numerical Simulation.

In this study, the wetting behaviors of single droplet on a micro square-post patterned surface with different geometrical parameters are investigated theoretically and numerically. A theoretical model is proposed for the prediction of wetting transition from the Cassie to Wenzel regimes. In addition, due to the limitation of theoretical method, a numerical simulation is performed, which helps get a view of dynamic contact lines, detailed velocity fields, etc., even if the droplet size is comparable with the scale of the surface micro-structures. It is found that the numerical results of the liquid drop behaviours on the square-post patterned surface are in good agreement with the predicted values by the theoretical model.

Phase-field-based lattice Boltzmann model for incompressible binary fluid systems with density and viscosity contrasts.

A lattice Boltzmann model (LBM) is proposed based on the phase-field theory to simulate incompressible binary fluids with density and viscosity contrasts. Unlike many existing diffuse interface models which are limited to density matched binary fluids, the proposed model is capable of dealing with binary fluids with moderate density ratios. A new strategy for projecting the phase field to the viscosity field is proposed on the basis of the continuity of viscosity flux. The new LBM utilizes two lattice Boltzmann equations (LBEs): one for the interface tracking and the other for solving the hydrodynamic properties. The LBE for interface tracking can recover the Chan-Hilliard equation without any additional terms; while the LBE for hydrodynamic properties can recover the exact form of the divergence-free incompressible Navier-Stokes equations avoiding spurious interfacial forces. A series of 2D and 3D benchmark tests have been conducted for validation, which include a rigid-body rotation, stationary and moving droplets, a spinodal decomposition, a buoyancy-driven bubbly flow, a layered Poiseuille flow, and the Rayleigh-Taylor instability. It is shown that the proposed method can track the interface with high accuracy and stability and can significantly and systematically reduce the parasitic current across the interface. Comparisons with momentum-based models indicate that the newly proposed velocity-based model can better satisfy the incompressible condition in the flow fields, and eliminate or reduce the velocity fluctuations in the higher-pressure-gradient region and, therefore, achieve a better numerical stability. In addition, the test of a layered Poiseuille flow demonstrates that the proposed scheme for mixture viscosity performs significantly better than the traditional mixture viscosity methods.

First Report of Fusarium oxysporum Causing Soft Fruit Rot Disease of Gray Jujube (Zizyphus jujuba) in China.

Gray Jujube, Zizyphus jujuba Mill., is a fruit crop unique to China that produces small fruit of high nutritional value with potential health benefits (2). In mid-September 2011, a fruit rot affecting approximately 10% of gray jujube fruit was observed in Xinzheng Date Garden, Henan Province, China. The diseased fruits exhibited small, oval, pale reddish brown lesions that expanded into clear concentric rings. Over time, the superficial lesions developed into soft rot affecting the whole fruit that produced a pungent odor. A putative Fusarium sp. was isolated by a single spore isolations from conidiophores produced on the decaying fruit. The isolated colonies first appeared on potato dextrose agar (PDA) as white to light yellow, then turned light pink. Falciform macroconidia were produced on PDA and were straight to slightly curved, usually 3-septate, short or medium long, 15.0 to 28 × 2.5 to 4.0 µm, with a curved apical cell and foot shaped to pointed basal cell. Microconidia were produced in false heads on Synthetic Nutrient-poor Agar (SNA), and were oval, 0-septate, 5.0 to 9.5 × 1.5 to 2.8 µm. Phialides were cylindrical and ranged from 7.0 to 20.0 × 0.7 to 1.4 µm. Chlamydospores were produced singularly and in pairs (1). Pathogenicity of the putative Fusarium sp. was evaluated by surface-sterilizing fresh gray jujubes on a healthy tree field and inoculating by placing a mycelial plug of the Fusarium sp. culture in contact with the fruit. An equal number of fresh gray jujube fruits were placed in contact with non-colonized PDA plugs to serve as a control. Each jujube fruit was wounded three times to create three holes close together using a steel needle (0.5 mm diameter), before inoculation with an agar plug. All the branches with inoculated fruits were enclosed in a clear plastic bag to maintain humidity and prevent cross contamination. After 3 days, inoculated jujubes exhibited the similar symptoms to those originally observed on the naturally infected fruits. Colonies resembling the Fusarium sp. isolated from the original lesions were obtained from each of the symptomatic fruits. Fruit inoculated with un-colonized PDA plugs remained asymptomatic and no fungus was isolated from these fruit. Koch's postulates were repeated three times with the same results. Based on the morphological characteristics, the Fusarium sp. was identified as F. oxysporum (1). The identity of the isolate was confirmed to be F. oxysporum by DNA sequencing of the elongation factor 1-alpha (EF-1a) gene (GenBank Accession No. KC796007), which was 99% homologous to those of other F. oxysporum isolates (JF430187 and JF430188). To our knowledge, this is the first report of F. oxysporum causing soft rot in fresh gray jujubes in Henan. This disease affects the yield and quality of fresh gray jujubes and potentially may threaten the jujube industry. References: (1) J. F. Leslie and B. A. Summerell. The Fusarium Laboratory Manual, 2006. (2) J. Sheng et al. Acta Hortic. 620:203, 2003.