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25 July 2016, Volume 33 Issue 4 Previous Issue    Next Issue

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Numerical Methods for Linear Global Stability of Magnetohydrodynamic Duct Flows HU Jun, LIU Chan, ZHANG Nianmei, NI Mingjiu 2016, 33(4): 379-390.  Abstract ( )   HTML ( )   PDF (3814KB) ( )   Spectral Chebyshev collocation method and high-order FD-q finite difference method are used for global instability analysis of magetohydrodynamic(MHD) duct flows and compared for their merits and drawbacks. Spectral Chebyshev collocation method has faster convergence rate and high-order accuracy, while it needs to construct full general eigenvalue matrix which would consume large memory storage and a great deal of computational cost. High-order FD-q finite difference method adopts modified Chebyshev collocation points as discretization mesh grids based on Kosloff-Tal-Ezer transformation. FD-q method can maintain high convergence rate of mesh grids, and resulted general eigenvalue matrix is very sparse and can be stored with sparse matrix, which greatly reduces computational resource. In contrast to traditional spectral collocation method, non-uniform mesh based FD-q method obtains remarkable progress on computational efficiency, which is further demonstrated by computation of linear optimal transient growth for MHD duct flows.

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Numerical Study on Unsteady Wave Patterns Produced by Particle Injection in Pipe Flows YIN Jingyue, LUO Xisheng 2016, 33(4): 391-398.  Abstract ( )   HTML ( )   PDF (2549KB) ( )   We investigate numerically unsteady wave patterns causing by injecting particles in one-dimensional pipe flows. Numerical simulations are performed using two-dimensional and axisymmetric vectorized adaptive solver. Coupling interaction of particles and flow and variation of flow parameters are highlighted. It is found that several kinds and intensities of wave patterns induced at different particle temperature and flow velocity are shown. We discuss wave patterns resulting by adding mass and heating interaction. Physics parameters in these flow field regions are given. In addition, phase diagrams about intensity of wave patterns are obtained to show flow field influenced by changing parameters.

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Lattice Boltzmann Study on Influence of Chemical Reaction on Mixing of Miscible Fluids with Viscous Instability in Porous Media LEI Timan, MENG Xuhui, GUO Zhaoli 2016, 33(4): 399-409.  Abstract ( )   HTML ( )   PDF (4015KB) ( )   Using Lattice Boltzmann method on GPU, viscous fingering of chemical fluids in porous media is simulated at pore scale. Influence of chemical reaction on fluid mixing is quantified. A one-variable chemical model admitting two stable states is adopted and a homogeneous artificial medium is generated by Quartet Structure Generation Set (QSGS) method. It shows that chemical reaction makes fingering interfaces sharp, restrains fluid mixing, and causes demixing. Influence is enhanced with increase of chemical reaction rate.

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Inverse Problems in Vibration for Difference Discrete Systemsof a Horizontal Bar Structure HE Min, ZHANG Lihua, WANG Qishen 2016, 33(4): 410-418.  Abstract ( )   HTML ( )   PDF (932KB) ( )   Inverse mode problem of a horizontal bar structure, a single branch structure of a rod-beam-rod system, is investigated. Sign-oscillatory properties of inherent vibration stiffness matrix of discrete horizontal bar structure are shown mathematically. In addition, qualitative properties of frequencies and modes are introduced. Physical parameters of horizontal bar structure are constructed from two sets of displacement or strain modes and corresponding circular frequencies. Several numerical examples are given. A particular inverse mode problem is discussed, where structure parameters of horizontal bar are symmetrical for geometrical symmetry axis. It shows that formulation of inverse problems is reasonable and solution method is validated.

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Thermo-elastic Singularity Analysis on V-notches in Orthotropic Materials YAO Shanlong, CHENG Changzheng, NIU Zhongrong 2016, 33(4): 419-426.  Abstract ( )   HTML ( )   PDF (1111KB) ( )   Thermo-elastic singularities of V-notches in orthotropic materials are studied. By introducing series asymptotic expansions of physics fields near notch tip, stress and flux equilibrium equations are transformed into characteristic ordinary differential equations with respect to singularity orders. Singularity orders and corresponding characteristic angular functions can be derived synchronously as interpolating matrix method is introduced to solve characteristice quations. The method evaluates stress and flux singularity orders at the same time. Numerical results show that it has high accuracy and strong adaptability.

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Analysis on Heat Transfer Coefficient of a PCM-glazed Unit LIU Changyu, LI Zaiwu, LI Dong 2016, 33(4): 427-433.  Abstract ( )   HTML ( )   PDF (2146KB) ( )   A coupled heat transfer model of phase change, radiation and heat conduction at steady state under solar irradiation in a semitransparent PCM-glazed unit was developed. Interior energy transfer of PCM-glazed unit was simulated with controlling volume method and Bouguer-Beer Law. Effects of radiation physical parameters, internal and external environment on heat transfer coefficient were investigated.It shows that it is necessary to consider semitransparent property of PCM-glazed unit as calculating heat transfer coefficient.Except for radiation physical property and environment, liquid fraction and light transmittance of PCM affect heat transfer coefficient as well.

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3D Simulation of External SGEMP of Cylinder SUN Huifang, ZHANG Fang, DONG Zhiwei 2016, 33(4): 434-440.  Abstract ( )   HTML ( )   PDF (2913KB) ( )   To study system-generated electromagnetic pulse(SGEMP) produced by complex model, a 3D particle in cell (PIC) code is exploited. A function module is appended to characterize cosine angular distribution and exponential energy spectra of photoelectron. For validation, external SGEMP effects induced by photoelectrons emitted from cylinder top surface is simulated and are compared with those by 2D code from literature. Subsequently, external SGEMP effects induced by photoelectrons emitted from half-side surface of a cylinder are studied. It shows that intense of electric field could get 56 kV·m-1 and magnetic field is 3.0×10-6T as emitting current is 3.3 A.

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Particle Simulation on Mutiple Wave Heating of Ions with Low-frequency Alfvén Waves LI Fuyi, XIANG Dong, GONG Xueyu, LU Xingqiang 2016, 33(4): 441-446.  Abstract ( )   HTML ( )   PDF (2147KB) ( )   Heating of magnetized plasma through one towards mutiple shear Alfvén waves with low frequency propagating along background magnetic field is studied with test particle simulation.It shows that mutiple waves whose frequencies match resonance condition lead to significantly efficiency heating by strengthen non-resononce process. With evolution of heating, mutiple waves turn to modulation wave. As frequencis of mutiple waves are close wave packets are created in transverse direction. A great ion temperature anisotrophy is produced and after that randomization process is stengthened either. Efficiency of stochastic heating process is also enhanced.It can be used in controling non-resonance and stochastic heating process by changing frequencise of mutiple low frequency waves.

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Electron Cyclotron Current Drive in Tokamak Plasma with Different Equilibrium Configuration ZHONG Yijun, GONG Xueyu, LI Xinxia, LI Jingchun 2016, 33(4): 447-452.  Abstract ( )   HTML ( )   PDF (1542KB) ( )   With given total toroidal current and central current density of plasma, temperature, density and magnetic field profiles of tokamak plasma with different elongation and triangularity are obtained numerically with Grad-Shafranov equation. Electron cyclotron wave ray trajectories and current drive in configurations are investigated with Fokker-Planck equation incorporated into a ray tracing code. It shows that as electron cyclotron wave of X-mode are launched from top, rays propagate toward low-field side with increasing elongation. As electron cyclotron wave are launched from mid-plane and low-field-side, high quotient power deposition is obtained with greater elongation, and driven current profile is close to central plasma with increase of triangularity. Current drive profile moves toward central plasma and peak current density increases with decreasing poloidal or toroidal injection angle.

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Photoelectron Spectra of Four-Level Ladder Molecules: Effect of Femtosecond Laser Parameters LI Yuehua, GUO Wei 2016, 33(4): 453-459.  Abstract ( )   HTML ( )   PDF (2112KB) ( )   Autler-Townes (AT) splitting in photoelectron spectra of four-level ladder K2 molecule driven by three laser pulses is investigated with time-dependent wave packet approach. Dependence of AT splitting on second laser pulse is studied. Photoelectron spectra show triple splitting with symmetric profiles in resonance, while triple splitting with asymmetric profiles is transformed into double splitting gradually in nonresnance. Three peaks shift to lower energy differently as laser wavelength increases. Splitting between two sideband peaks does not vary with laser wavelength, but increases with increasing laser intensity. These results are of importance for molecular spectroscopy. It stimulates theoretical studies from first principles and provides basis for realizing optical control of molecules.

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Van der Waals Interaction Coefficients C3 Between Excited State|62P3/2F>(F=2, 3, 4, 5) of 133Cs Atoms and Perfect Surface of a Metal in Hyperfine Atomic Levels WEI Naiping, ZHAO Xiaoxia, LI Li, ZHANG Yanpeng, LI Yuanyuan, XU Kewei 2016, 33(4): 460-466.  Abstract ( )   HTML ( )   PDF (589KB) ( )   Coefficients C3 of hyperfine levels of excited states|62P3/2 F> (F=2, 3, 4, 5) of 133Cs atom are calculated with irreducible tensor method and van der Waals (vdW) interaction between alkali atoms and perfect surface of a metal. C3 of|62P3/2F>(F=2, 3, 4, 5) we obtained are 4.3385 kHz·μm3, 4.3619 kHz·μm3, 4.3680 kHz·μm3, and 4.3467 kHz·μm3. Our data are compared with other theoretical data and experimental data. It shows that they are reliable.

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A Study on Stability of Alloyed Cementite WANG Hongjun, LIU Hongyu, LU Jianduo, LIN Chong, XU Hongbing 2016, 33(4): 467-476.  Abstract ( )   HTML ( )   PDF (1365KB) ( )   With empirical electronic theory of solids and molecules (EET), actual model for unit cell of cementite was built. A statistical method was applied to compute valence electron structure (VES) of cementite of θ-Fe3C with specified number of Fe atoms substituted by alloyed atom of M(Cr, V, W, Mo, Mn). By definition stability factor, stability of alloyed cementite with different type, number and site of Fe atoms substituted were calculated and analysized. It shows that density of lattice electron, symmetry of bonds and bond energy have great influence on stability of alloyed cementite. It is more stable as M substitutes for Fe2 than Fe1. Alloyed cementite is the most stable as Cr, Mo, W and V substitutes for 2 atoms of Fe2 at sites of No.2 and 3 or No.6 and 7. Stability of alloyed cementite decreases in order of W, Cr, V, Mo and Mn.

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Ferromagnetism in Defective TiO2: First-principles Calculations ZONG Zhaocun, ZHANG Cunxi, QIN Xiaoping 2016, 33(4): 477-482.  Abstract ( )   HTML ( )   PDF (5108KB) ( )   Coexistence of Ti vacancies and O vacancies is calculated to study ferromagnetic ordering in undoped rutile TiO2. It shows that O vacancy (VO) favors magnetic state in undoped TiO2. Spin polarization induced by VO is more localized than that induced by VTi, which is the reason that FM coupling of two VO is weaker than that of two VTi . FM coupling of two VTi is strengthened as VO is introduced. Long-range FM coupling between two separate VTi is mediated by electrons introduced by VO. Magnetic moments induced by two VO quenched as VTi is introduced. VO contributes magnetic moment only if the number of VO is more than twice that of VTi. It is in quantitative agreement with experimental results that VO can promote ferromagnetic ordering, and magnetic moment increase with increase of the number of VO.

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Phonon Structure and Electron-phonon Interaction in Bi4Se3 Film: First-principles Study LIU Xia, DU Xiao, ZHANG Junjie, HUANG Guiqin 2016, 33(4): 483-489.  Abstract ( )   HTML ( )   PDF (2478KB) ( )   Based on density functional perturbation theory, phonon properties and electron-phonon interaction in Bi4Se3 film system are studied with first-principles calculations. It shows that dynamic of Bi4Se3 film system for two terminations is stable. There exists mismatch in projected phonon density of states between Bi2 bilayer and Bi2Se3quintuple layer. It prevents part phonons to transport in Bi4Se3 film, which leads to thermal conductivity reduce and improves thermoelectric performance of material. Besides, electron-phonon coupling constant of Bi4Se3 film in two kinds of termination are small (about 0.278), which is in favour of electronic device in room temperature.

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Theoretical Study on Electronic Structure and Optical Properties of GaN:TM(TM=V, Cr, Mn, Fe, Co, Ni) DONG Yanfeng, LI Ying 2016, 33(4): 490-498.  Abstract ( )   HTML ( )   PDF (6320KB) ( )   Electronic structure and optical properties of GaN systems doped with transition metals (GaN:TM, TM=V, Cr, Mn, Fe, Co, Ni) are studied with first-principles calculations. Influences of transition metals on electronic structure and optical properties are discussed. It shows that doped materials are direct semiconductors with half-metal property except Fe-doped material. Transition metal impurity introduces defect levels in energy gap of GaN, which is contributed by 3d electron states of transition metals. For GaN:V, Cr, Mn, Co, absorption peaks appear near defect level in low energy region. These peaks can be attributed to transiton between 3d electrons and N-2p electrons.

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Simulation Analysis of Routes to Chaos in Optoelectronic Delay Feedback Systems BAO Xiurong 2016, 33(4): 499-504.  Abstract ( )   HTML ( )   PDF (1826KB) ( )   Response time series of nonlinear optoelectronic delay feedback system is numerical analyzed. Broadband pass filter is inserted in feedback loop of model. Mathematical model of nonlinear optoelectronic delay feedback system is set up. Two routes to chaos are numerical analyzed by adjusting parameters of system. At specific φ, under condition of low feedback gain, fast square wave signal or slow cycle oscillation signal is observed. With increase of feedback gain, more complex periodic signal or chaos breather phenomenon is appeared. At higher feedback gain, output of system is from different dynamic regimes into chaos.