Yang Y.,Rensselaer Polytechnic Institute |
Huang H.,Rensselaer Polytechnic Institute |
Huang H.,University of Connecticut |
Xiang S.K.,Institute of Fluid Physics |
Chason E.,Brown University
Applied Physics Letters | Year: 2010
The diffusion of adatoms into grain boundaries (GBs) of polycrystalline thin film during vapor deposition affects the stress that develops and the film's subsequent performance. This Letter reports a proposed mechanism of modifying the stress by controlling adatom diffusion into GBs through the use of surfactants. Based on polycrystalline kinetic Monte Carlo simulations of Cu 〈 111 〉 thin films with In surfactant, the authors demonstrate that the proposed mechanism is feasible. Further, the authors show that the reduction is due to the decrease in effective adatom diffusivity, which dominates over the increase in adatom concentration. © 2010 American Institute of Physics.
Wang Y.,Ningbo University |
He H.,Institute of Fluid Physics |
Wang L.,Ningbo University
Mechanics of Materials | Year: 2013
A Critical Damage Evolution (CDE) model considering void growth and coalescence is proposed for describing the dynamic tensile spall of ductile metals sustaining intense dynamic loading. Based on the percolation hypothesis, two physical parameters, named the critical void coalescence damage D c and the critical fracturing damage Df, are suggested to indicate the critical behavior of dynamic tensile fracture, namely the onset of void coalescence and the occurrence of catastrophic fracture, respectively. Finite element simulations of plate impact and sliding detonation tests have been carried out and compared to the experiments for steel. From the results obtained, we demonstrate that spall failure of ductile metals is dependent on these two critical damage parameters, which are intrinsic material parameters and thus independent of impact stress and strain rate. © 2012 Elsevier Ltd. All rights reserved.
Zhang X.,Institute of Fluid Physics
Computers and Fluids | Year: 2013
Based on the single-mode potential model of Jacobs and Rikanati, Firstly, a viscous single-mode bubble evolution model of Rayleigh Taylor instability (RTI) is developed in this study. Viscous effects of RTI's early stage growth for low Atwood number have been explained. In addition, direct numerical simulations of single mode RTI are studied with Navier-Stokes equations and a transport-diffusive equation for miscible fluids, in which these equations are discritized with discontinuous Galerkin (DG) spectral element method. The turbulent mixing of RTI has kinetic energy dissipation, and the dissipation rate is determined by the inertial and viscous effects. Therefore, the numerical techniques must include a dissipation mechanism for kinetic energy. For this reason, the high accurate spectral element method is employed in this study. Agreement between the theoretical model and the numerical results shows that simulations of RTI is feasible using the mathematical miscible fluid model. The results also suggest that a high order numerical method may provide the capability of simulating small scale fluctuations in turbulent flows with RTI. © 2013 Elsevier Ltd.
Wang X.-M.,CAS Beijing National Laboratory for Molecular |
Wang C.-H.,Peking University |
Wang C.-H.,Institute of Fluid Physics |
Kuang X.-J.,Sun Yat Sen University |
And 3 more authors.
Inorganic Chemistry | Year: 2012
A novel oxonitridosilicate phosphor host Sr 3Si 2O 4N 2 was synthesized in N 2/H 2 (6%) atmosphere by solid state reaction at high temperature using SrCO 3, SiO 2, and Si 3N 4 as starting materials. The crystal structure was determined by a Rietveld analysis on powder X-ray and neutron diffraction data. Sr 3Si 2O 4N 2 crystallizes in cubic symmetry with space group Pa3̄, Z = 24, and cell parameter a = 15.6593(1) Å. The structure of Sr 3Si 2O 4N 2 is constructed by isolated and highly corrugated 12 rings which are composed of 12 vertex-sharing [SiO 2N 2] tetrahedra with bridging N and terminal O to form three-dimensional tunnels to accommodate the Sr 2+ ions. The calculated band structure shows that Sr 3Si 2O 4N 2 is an indirect semiconductor with a band gap ≈ 2.84 eV, which is close to the experimental value ≈ 2.71 eV from linear extrapolation of the diffuse reflection spectrum. Sr 3-xSi 2O 4N 2:xEu 2+ shows a typical emission band peaking at ∼600 nm under 460 nm excitation, which perfectly matches the emission of blue InGaN light-emitting diodes. For Ce 3+/Li +-codoped Sr 3Si 2O 4N 2, one excitation band is in the UV range (280-350 nm) and the other in the UV blue range (380-420 nm), which matches emission of near-UV light-emitting diodes. Emission of Sr 3-2xSi 2O 4N 2:xCe 3+,xLi + shows a asymmetric broad band peaking at ∼520 nm. The long-wavelength excitation and emission of Eu 2+ and Ce 3+/Li +-doped Sr 3Si 2O 4N 2 make them attractive for applications in phosphor-converted white light-emitting diodes. © 2012 American Chemical Society.
Zhang X.,Institute of Fluid Physics |
Zhang X.,University of Wyoming |
Stanescu D.,University of Wyoming
Computers and Fluids | Year: 2010
This paper studies round jet with large eddy simulation (LES) method, in which spectral element technique is used as spacial discritization for the large eddy simulation Navier-Stokes equations. A local spectral discretization associated with Legendre polynomials is employed on each element of the structured mesh, which allows for high accurate simulations of turbulent flows. Discontinuities across the interfaces of the elements are resolved using a Riemann solver. An isoparametric representation of the geometry is implemented, with boundaries of the domain discretized to the same order of accuracy as the solution, and explicit low-storage Runge-Kutta methods are used for time integration. LES results of round jet are presented, in which the instantaneous and statistical turbulence structures of the round jet have been captured. The probability density function, and the spectral density function of the round jet that can reflect properties of turbulence have also been estimated. The work serves the purpose of allowing fast, convenient computations and comparisons with theoretical results and the ultimate goal is to develop it into an LES code featuring spectral accuracy with minimum dissipation and dispersion, a valuable tool for round jet computations. © 2009 Elsevier Ltd. All rights reserved.