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Wan Z.,Hefei University of Technology | Zhou L.,Chinese Academy of Engineering Physics | Yang H.,Hefei University of Technology | Sun D.,Hefei University of Technology
Physics of Fluids

Large eddy simulation is performed for investigating the local and far-field behaviors of free and swirling jets at moderate Reynolds number. By solving compressible boundary layer equations, the inflow profiles with different swirl number are calculatedthen their stability characteristics are analyzed based on linear stability theory. The amplification rates of swirling jets are higher than the free one, particularly for higher or negative azimuthal wavenumber modes. Multiple unstable modes are superimposed to construct inflow forcing. The quantities of flow and acoustic are presented and compared against the results of existed experiments and other computations, besides, the comparisons are also made among themselves. For swirling jets, the spreadings of jet half-width and vorticity thickness at the initial and transition stage are enhanced, but they are surpassed by the free jet at turbulent mixing stage. In all cases, the development of mixing layer initially is greatly influenced by frequencies f0 and f0/2 associated with upstream forcing. As the swirl intensity is increased, the growth rates of fluctuation quantities on the centerline and the nozzle lip line are raised, but the peak levels on the centerline are reduced substantially. In swirling jets, the strength of vortex pairing is decreasedthe pairing noise is weakened correspondingly. The overall sound pressure levels are lower than that of the free jet at all observation angles (φ{symbol})about 3 decibels (dB) is reduced at φ{symbol} ≃ 30° in the strong swirling case at a distance of 60 radii. The Fourier analyses of pressure and acoustic sources show that the modes are varied greatly, which suggests that the noise reduction should be corresponding to the change of instability waves. © 2013 AIP Publishing LLC. Source

Lv Z.-L.,Sichuan University | Lv Z.-L.,Henan University of Science and Technology | Cheng Y.,Sichuan University | Chen X.-R.,Sichuan University | Ji G.-F.,Chinese Academy of Engineering Physics
Computational Materials Science

CdSiP2 is regarded to be a promising material for future technical applications, but many of its properties are still not well studied. In this work, electronic, bonding, elastic properties and intrinsic hardness of CdSiP2 are investigated by performing first principles calculations within the framework of generalized gradient approximation. Calculations indicate that CdSiP2 is a direct-gap semiconductor with a gap value of 1.22 eV located at the Γ-point. Combined with the density of states, the characteristics of the band structure have been analyzed and their origins have been specified, which reveal that sp3 hybridization plays an important role in the formation of the crystal. Charge analyses disclose that CdSiP2 is a crystal with ionic and covalent properties. The calculated intrinsic hardness of CdSiP2 is 10.05 GPa, agreeing well with the experimental value of 10.5 GPa. Its bulk modulus and elastic constants, together with its elastic anisotropy, are also computed and analyzed. The obtained elastic constants are larger than other theoretical ones, as a result, the bulk modulus deduced gives a value of 80.99 GPa, which is more reasonable compared with the experimentally derived value and other theoretical ones. © 2013 Elsevier B.V. All rights reserved. Source

Chen Y.,Chinese Academy of Engineering Physics
Journal of Chromatography A

A set of accurate expressions of elution-curve moments are derived from the moments of residence time and displacement in a step based on probability theory. Then the problems about residence time and displacement in a step of a solute molecule in the porous layer of capillary columns and in the moving mobile phase are described by a set of mass-balance equations respectively. The set of equations are solved in Fourier-Laplace domain, and the characteristic functions of residence time of a step, as well as the moments, are obtained by means of computing software Mathematica. At last, using numerical inverse Laplace transform, the elution curves for various conditions are calculated. In the case of large desorption constant the results entirely coincide with those of mass-balance-equation theory and in the case of small desorption constant they are equivalent to those of stochastic theory. © 2011 Elsevier B.V. Source

Hu J.,Jilin University | Dong X.,Jilin University | Dong X.,Chinese Academy of Engineering Physics | Tosto S.,ENEA
Journal of the American Ceramic Society

High resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) techniques were used to examine the crystal structure of TiB ceramic powder synthesized by a Ti-Boronizing method. The HRTEM analysis revealed that the synthesized titanium boride has fcc crystal structure, with titanium and boron atoms alternatively arranged like Na and Cl ions in NaCl-type lattice. The crystal structure of this boride phase, denoted as fcc-TiB in the paper, was confirmed also by XRD analysis and agrees with the data reported in the card PDF # 06-641. This card is present in the powder diffraction file (PDF) database, but seldom quoted in literature because the typical crystal structure of TiB that forms in situ as a phase is orthorhombic. The present work reports new experimental data on the crystal properties of pure fcc-TiB not yet reported in the literature. The lattice parameter of fcc-TiB, calculated from XRD analysis, is a 0=4.245 Å. © 2012 The American Ceramic Society. Source

Wang H.,Chinese Academy of Engineering Physics | Zhu H.,Chinese Academy of Engineering Physics
Nanoscale Research Letters

The size evolution of Pb nanoparticles (NPs) synthesized by ion implantation in an epitaxial Al film has been experimentally investigated. The average radius R of Pb NPs was determined as a function of implantation fluence f. The R(f) data were analyzed using various growth models. Our observations suggest that the size evolution of Pb NPs is controlled by the diffusion-limited growth kinetics (R 2∝f). With increasing implantation current density, the diffusion coefficient of Pb atoms in Al is evident to be enhanced. By a comparative analysis of the R(f) data, values of the diffusion coefficient of Pb in Al were obtained. © 2014 Wang and Zhu; licensee Springer. Source

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