Paraelectric-ferroelectric interface dynamics induced by latent heat transfer and irreversibility of ferroelectric phase transitions

The temperature gradients that arise in the paraelectric-ferroelectric interface dynamics induced by the latent heat transfer are studied from the point of view that a ferroelectric phase transition is a stationary, thermal-electric coupled transport process. The local entropy production is derived for a ferroelectric phase transition system from the Gibbs equation. Three types of regions in the system are described well by using the Onsager relations and the principle of minimum entropy production. The theoretical results coincides with the experimental ones.

Chemical composition and formation mechanisms in the cathode-electrolyte interface layer of lithium manganese oxide batteries from reactive force field （ReaxFF） based molecular dynamics

Lithium manganese oxide （LiMn2O4） is a principal cathode material for high power and high energy density electrochemical storage on account of its low cost, non-toxicity, and ease of preparation relative to other cathode materials. However, there are well-documented problems with capacity fade of lithium ion batteries containing LiMn2O4. Experimental observations indicate that the manganese content of the electrolyte increases as an electrochemical cell containing LiMn2O4 ages, suggesting that active material loss by dissolution of divalent manganese from the LiMn2O4 surface is the primary reason for reduced cell life in LiMn2O4 batteries. To improve the retention of manganese in the active material, it is key to understand the reactions that occur at the cathode surface. Although a thin layer of electrolyte decomposition products is known to form at the cathode surface, the speciation and reaction mechanisms of Mn^2＋ in this interface layer are not yet well understood. To bridge this knowledge gap, reactive force field （ReaxFF） based molecular dynamics was applied to investigate the reactions occurring at the LiMn2O4 cathode surface and the mechanisms that lead to manganese dissolution. The ReaxFFMD simulations reveal that the cathode-electrolyte interface layer is composed of oxida- tion products of electrolyte solvent molecules including aldehydes, esters, alcohols, polycarbonates, and organic radicals. The oxidation reaction pathways for the electro- lyre solvent molecules involve the formation of surface hydroxyl species that react with exposed manganese atoms on the cathode surface. The presence of hydrogen fluoride （HF） induces formation of inorganic metal fluorides and surface hydroxyl species. Reaction products predicted by ReaxFF-based MD are in agreement with experimentally identified cathode-electrolyte interface compounds. An overall cathode-electrolyte interface reaction scheme is proposed based on the molecular simulation results.

Towards real-time pilot-in-the-loop CFD simulations of helicopter/ship dynamic interface

This study presents the development of computationally efficient coupling of Navier–Stokes Computational Fluid Dynamics(CFD)with a helicopter flight dynamics model with the ultimate goal of real-time simulation of airwake effects in the helicopter/ship Dynamic Interface(DI).The flight dynamics model is free to move within a computational domain,where the main rotor forces are converted to source terms in the momentum equations of the CFD solution using an actuator disk model.Simultaneously,the CFD solver calculates induced velocities that are fed back to the simulation and affect the aerodynamic loads in the flight dynamics.The CFD solver models the inflow,ground effect and interactional aerodynamics in the flight dynamics simulation,and these calculations can be coupled with the solution of the external flow(e.g.,ship airwake effects).The simulation framework for fully-coupled pilot-in-the-loop(PIL)flight dynamics/CFD is demonstrated for a simplified shedding wake.Initial tests were performed with 0.38 million structured grid cells running on 352 processors and showed near-real-time performance.Improvements to the coupling interface are described that allow the simulation run at near-real-time execution speeds on currently available computing platforms.Improvements in computing hardware are expected to allow real-time simulations.

ACTUATION OF SLOSHING MODULATED FORCE AND MOMENT ON LIQUID CONTAINER DRIVEN BY JITTER ACCELERATIONS ASSOCIATED WITH SIEW MOTION IN MICROGRAVITY

The mathematical formulation of sloshing dynamics for a partially liquid filleddewar container driven by the gravity jitter acceleration associated with slew motion isstudied.Explicit mathematical expressions to manage jitter accelerption associated withslew motion which is acting on the fluid systems in microgravity are derived. Thenumerical computation of sloshing dymamics is based on the non-inertia framecontainer bound coordinate and the solution of time-dependent three-dimensionalformulations of partial differential equations subject to initial and boundary conditions.The numerical computation of fluid viscous stress forces and moment fluctuationsexerted on the dewar container driven by jitter acceleration associated with slew motion is investigated.

Study of Bone-screw Surface Fixation in Lumbar Dynamic Stabilization

Background： We aimed to use the animal model of dynamic fixation to examine the interaction of the pedicle screw surface with sun＇ounding bone, and determine whether pedicle screws achieve good mechanical stability in the vertebrae. Methods： Twenty-four goats aged 2-3 years had Cosmic pedicle screws implanted into both sides of the L2-L5 pedicles. Twelve goats in the bilateral dynamic fixation group had fixation rods implanted in L2-L3 and L4-L5. Twelve goats in the unilateral dynamic fixation group had fixation rods randomly fixed on one side of the lumbar spine. The side that was not implanted with fixation rods was used as a static control group. Results： In the static control group, new bone was formed around the pedicle screw and on the screw surthce. In the unilateral and bilateral dynamic fixation groups, large amounts of connective tissue formed between and around the screw threads, with no new bone formation on the screw surlhce; the pedicle screws were loose after the fixed rods were removed. The bone mineral density and morphological parameters of the region of interest （ROI） in the unilateral and bilateral dynamic fixation group were not significantly different （P 〉 0.05）, but were lower in the fixed groups than the static control group （P 〈 0.05）. This showed the description bone of the ROI in the static control group was greater than in the fixation groups. Under loading conditions, the pedicle screw maximum pull force was not significantly different between the bilateral and unilateral dynamic fixation groups （P 〉 0.05）： however the maximum pull force of the fixation groups was significantly less than the static control group （P 〈 0.01 ）. Conclusions： Fibrous connective tissue formed at the bone-screw interface tinder unilateral and bilateral pedicle dynamic fixation, and the pedicle screws lost mechanical stability in the vertebrae.

Phase-Field Models for Multi-Component Fluid Flows

In this paper,we review the recent development of phase-field models and their numerical methods for multi-component fluid flows with interfacial phenomena.The models consist of a Navier-Stokes system coupled with a multi-component Cahn-Hilliard system through a phase-field dependent surface tension force,variable density and viscosity,and the advection term.The classical infinitely thin boundary of separation between two immiscible fluids is replaced by a transition region of a small but finite width,across which the composition of the mixture changes continuously.A constant level set of the phase-field is used to capture the interface between two immiscible fluids.Phase-field methods are capable of computing topological changes such as splitting andmerging,and thus have been applied successfully to multi-component fluid flows involving large interface deformations.Practical applications are provided to illustrate the usefulness of using a phase-field method.Computational results of various experiments show the accuracy and effectiveness of phase-field models.

Mesoscopic model for binary fluids

We propose a model for studying binary fluids based on the mesoscopic molecular simulation technique known as multiparticle collision, where the space and state variables are continuous, and time is discrete. We include a repulsion rule to simulate segregation processes that does not require calculation of the interaction forces between particles, so binary fluids can be described on a mesoscopic scale. The model is conceptually simple and computationally efficient; it maintains Galilean invariance and conserves the mass and energy in the system at the micro- and macro-scale, whereas momentum is conserved globally. For a wide range of temperatures and densities, the model yields results in good agreement with the known properties of binary fluids, such as the density profile, interface width, phase separation, and phase growth. We also apply the model to the study of binary fluids in crowded environments with consistent results.

Modeling nanoscale ice adhesion

Anti-icing is crucial for numerous instruments and devices in low temperature circum- stance. One of the approaches in anti-icing is to reduce ice adhesion strength, seeking spontaneous de-icing processes by natural forces of gravity or by winds. In order to enable tai- lored surface icephobicity design, research requires a good theoretical understanding of the atomistic interacting mechanisms between water/ice molecules and their adhering substrates. Herein, this work focuses on using atomistic modeling and molecular dynamics simulation to build a nanosized ice-cube adhering onto silicon surface, with different contact modes of solid-solid and solid-liquid-solid patterns. This study provides atomistic models for probing nanoscale ice adhesion mechanics and theoretical platforms for explaining experimental results.

Promising commercial reinforcement to the nanodiamond/epoxy composite by grafting ammonium ions

A simple, economic, efficient and eco-friendly nanodiamond （ND） modifying method to reinforce the ND]epoxy composite for the industrialization of the high-performance ND/epoxy composite is always desired. In the present work, the ND was successfully modified only using aqueous ammonia through an easy-to-operate method by replacing the hydrogen atoms in the carboxyl group with ammonium ions. Ammonia, which is the only pollutant in the process, could be recycled. The modified ND/epoxy composite showed an overwhelming advantage over the neat epoxy or the ND/epoxy composite in storage modulus in their glassy state without any degradation of tensile strength, hardness and fracture toughness.

Gaussian Beam Summation for Diffraction in Inhomogeneous Media Based on the Grid Based Particle Method

We develop an efficient numerical method to compute single slit or double slit diffraction patterns from high frequency wave in inhomogeneous media.We approximate the high frequency asymptotic solution to the Helmholtz equation using the Eulerian Gaussian beam summation proposed in[20,21].The emitted rays from a slit are embedded in the phase space using an open segment.The evolution of this open curve is accurately computed using the recently developed Grid Based Particle Method[24]which results in a very efficient computational algorithm.Following the grid based particle method we proposed in[23,24],we represent the open curve or the open surface by meshless Lagrangian particles sampled according to an underlying fixed Eulerian mesh.The end-points of the open curve are tracked explicitly and consistently with interior particles.To construct the overall wavefield,each of these sampling particles also carry necessary quantities that are obtained by solving advection-reaction equations.Numerical experiments show that the resulting method can model diffraction patterns in inhomogeneous media accurately,even in the occurrence of caustics.