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Study on lattice vibrational properties and Raman spectra of Bi_2Te_3 based on density-functional perturbation theory

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Chinese Physics B 2014年第8期23卷 420-425页

作者：冯松科李双明傅恒志 state Key Laboratory of Solidification Processing Northwestern Polytechnical University (NPU)

We present a variational density-functional perturbation theory （DFPT） to investigate the lattice dynamics and vibra- tional properties of single crystal bismuth telluride material. The phonon dispersion curves and phonon density of states （DOS） of the material were obtained. The phonon dispersions are divided into two fields by a phonon gap. In the lower field, atomic vibrations of both Bi and Te contribute to the DOS. In the higher field, most contributions come from Te atoms. The calculated Born effective charges and dielectric constants reveal a great anisotropy in the crystal. The largest Born effective charge generates a significant dynamic charge transferring along the c axis. By DFPT calculation, the greatest LO-TO splitting takes place in the infrared phonon modes and reaches 1.7 THz in the Brillouin zone center. The Raman spectra and peaks corresponding to respective atomic vibration modes were found to be in good agreement with the experimental data.

关键词： density-functional perturbation theory Bi2Te3 material lattice vibrational properties Raman spectra

Simulation study on factors influencing the entrainment behavior of liquid steel as bubbles pass through the steel/slag interface

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International Journal of Minerals,Metallurgy and Materials 2016年第5期23卷 511-519页

作者： Xiang Li Yan-ping Bao Min Wang Lu Lin state Key Laboratory of Advanced Metallurgy University of Science and Technology Beijing

In this study, a water/silicone oil interface was used to simulate the steel/slag interface in a converter. A high-speed camera was used to record the entrainment process of droplets when air bubbles were passed through the water/silicone oil interface. Motion parameters of the bubbles and droplets were obtained using particle kinematic analysis software, and the entrainment rate of the droplets was calculated. It was found that the entrainment rate decreased from 29.5% to 0 when the viscosity of the silicone oil was increased from 60 mPa.s to 820 mPa.s in the case of bubbles with a 5 mm equivalent diameter passing through the water/silicone oil interface. The results indicate that in- creasing the viscosity of the silicone oil is conducive to reducing the entrainment rate. The entrainment rate increased from 0 to 136.3% in the case of silicone oil with a viscosity of 60 mPa.s when the equivalent diameter of the bubbles was increased from 3 mm to 7 ram. We there- fore conclude that small bubbles are also conductive to reducing the entrainment rate. The force analysis results for the water colmnn indicate that the entrainment rate of droplets is affected by the velocity of the bubble passing through the water/silicone oil interface and that the en- trainment rate decreases with the bubble velocity.

关键词： steelmaking bubbles interfaces entrainment influencing factors simulation studies

Calculation on Cylinder Pressure Fluctuation by Using the Wave Equation in KIVA Program

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Chinese Journal of Mechanical Engineering 2012年第2期25卷 362-369页

作者： WEI Haiqiao WEI Jingsi SHU Gequn state Key Laboratory of Engines Tianjin UniversityTianjin 300072China

Cylinder pressure fluctuation during combustion process of internal combustion engine is closely related to combustion noise and *** current studies are based on cylinder pressure test to obtain information on combustion noise and knock,but there is little for simulation of combustion pressure *** on effects of combustion process in the combustion chamber on cylinder pressure by using wave equation,the mechanism of pressure fluctuation during combustion is researched with three-dimensional acoustic wave equation and flow field model of KIVA *** cylinder pressure fluctuation curve,temperature field and acoustic field are obtained from the coupled calculation of the wave equation and KIVA *** frequency spectrum analysis is taken with the cylinder pressure oscillation of cylinder pressure measured and *** calculation result is consistent with the experimental *** indicates that the cylinder pressure fluctuation can be correctly calculated with the wave *** of calculation results of temperature field and acoustic field shows that sound field changes faster than flame propagates,and distribution of sound field is more *** pressure oscillation in the diesel engine is under highly unstable *** indicates that the combination of cylinder pressure fluctuation model and combustion model is an effective method to study the pressure oscillations and a new method to study the combustion noise and knock.

关键词： combustion pressure oscillation acoustic pressure knock wave equation

Energy Transfer Mechanism and Probability Analysis of Submarine Pipe Laterally Impacted by Dropped Objects

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China Ocean Engineering 2016年第3期30卷 319-328页

作者：梁静余建星余杨 W.Lam 赵羿羽段晶辉 state Key Laboratory of Hydraulic Engineering Simulation and Safety Tianjin University

Energy transfer ratio is the basic-factor affecting the level of pipe damage during the impact between dropped object and submarine pipe. For the purpose of studying energy transfer and damage mechanism of submarine pipe impacted by dropped objects, series of experiments are designed and carried out. The effective yield strength is deduced to make the quasi-static analysis more reliable, and the normal distribution of energy transfer ratio caused by lateral impact on pipes is presented by statistic analysis of experimental results based on the effective yield strength, which provides experimental and theoretical basis for the risk analysis of submarine pipe system impacted by dropped objects. Failure strains of pipe material are confirmed by comparing experimental results with finite element simulation. In addition, impact contact area and impact time are proved to be the major influence factors of energy transfer by sensitivity analysis of the finite element simulation.

关键词： impact pipe energy transfer quasi-static analysis FE simulation

pyGWBSE:a high throughput workflow package for GW-BSE calculations

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npj Computational Materials 2023年第1期9卷 2127-2136页

作者： Tathagata Biswas Arunima K.Singh Department of Physics Arizona State UniversityTempe 85287 AZUSA

We develop an open-source python workflow package,pyGWBSE to perform automated first-principles calculations within the GW-BSE(Bethe-Salpeter)***-BSE is a many body perturbation theory based approach to explore the quasiparticle(QP)and excitonic properties of *** approximation accurately predicts bandgaps of materials by overcoming the bandgap underestimation issue of the more widely used density functional theory(DFT).BSE formalism produces absorption spectra directly comparable with experimental *** package achieves complete automation of the entire multi-step GW-BSE computation,including the convergence tests of several parameters that are crucial for the accuracy of these *** is integrated with Wannier90,to generate QP bandstructures,interpolated using the maximally-localized wannier *** also enables the automated creation of databases of metadata and data,including QP and excitonic properties,which can be extremely useful for future material discovery studies in the field of ultra-wide bandgap semiconductors,electronics,photovoltaics,and photocatalysis.

关键词： automated python enable

Experimental Study of Nonlinear Behaviors of A Free-Floating Body in Waves

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China Ocean Engineering 2016年第3期30卷 421-430页

作者：贺铭任冰邱大洪 state Key Laboratory of Coastal and Offshore Engineering Dalian University of Technology

Nonlinear behaviors of a free-floating body in waves were experimentally investigated in the present study. The experiments were carried out for 6 different wave heights and 6 different wave periods to cover a relatively wide range of wave nonlinearities. A charge-coupled device （CCD） camera was used to capture the real-time motion of the floating body. The measurement data show that the sway, heave and roll motions of the floating body are all harmonic oscillations while the equilibrium position of the sway motion drifts in the wave direction. The drift speed is proportional to wave steepness when the size of the floating body is comparable to the wavelength, while it is proportional to the square of wave steepness when the floating body is relatively small. In addition, the drift motion leads to a slightly longer oscillation period of the floating body than the wave period of nonlinear wave and the discrepancy increases with the increment of wave steepness.

关键词： floating body nonlinear wave motion trajectory drift speed oscillation period

Impact of Typical Steady-state Conditions and Transient Conditions on Flow Ripple and Its Test Accuracy for Axial Piston Pump

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Chinese Journal of Mechanical Engineering 2015年第5期28卷 1012-1022页

作者： XU Bing HU Min ZHANG Junhui state Key Laboratory of Fluid Power Transmission and Control Zhejiang University

The current research about the flow ripple of axial piston pump mainly focuses on the effect of the structure of parts on the flow ripple. Therein, the structure of parts are usually designed and optimized at rated working conditions. However, the pump usually has to work in large-scale and time-variant working conditions. Therefore, the flow ripple characteristics of pump and analysis for its test accuracy with respect to variant steady-state conditions and transient conditions in a wide range of operating parameters are focused in this paper. First, a simulation model has been constructed, which takes the kinematics of oil film within friction pairs into account for higher accuracy. Afterwards, a test bed which adopts Secondary Source Method is built to verify the model. The simulation and tests results show that the angular position of the piston, corresponding to the position where the peak flow ripple is produced, varies with the different pressure. The pulsating amplitude and pulsation rate of flow ripple increase with the rise of pressure and the variation rate of pressure. For the pump working at a constant speed, the flow pulsation rate decreases dramatically with the increasing speed when the speed is less than 27.78% of the maximum speed, subsequently presents a small decrease tendency with the speed further increasing. With the rise of the variation rate of speed, the pulsating amplitude and pulsation rate of flow ripple increase. As the swash plate angle augments, the pulsating amplitude of flow ripple increases, nevertheless the flow pulsation rate decreases. In contrast with the effect of the variation of pressure, the test accuracy of flow ripple is more sensitive to the variation of speed. It makes the test accuracy above 96.20% available for the pulsating amplitude of pressure deviating within a range of ~6% from the mean pressure. However, with a variation of speed deviating within a range of ±2% from the mean speed, the attainable test accuracy o

关键词： axial piston pump flow ripple test accuracy steady-state condition transient condition wide operating ranges

High-temperature phase transition behavior and magnetocaloric effect in a sub-rapidly solidified La–Fe–Si plate produced by centrifugal casting

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Journal of Materials Science & Technology 2018年第8期34卷 1337-1343页

作者： Zhishuai Xu Yuting Dai Yue Fang Zhiping Luo Ke Han Changjiang Song Qijie Zhai Hongxing Zheng Laboratory for Microstructures Shanghai UniversityShanghai 200444China state Key Laboratory of Advanced Spedal Steel Shanghai UniversityShanghai 200444China Department of Chemistry and Physics FayetteviUe State UniversityFayettevilleNC28301USA National High Magnetic Field Laboratory Florida State UniversityTaUahasseeFL 32310USA

A sub-rapidly solidified LaFe11.6Si1.4 plate was fabricated directly from liquid by centrifugal casting method. The phase constitution, microstructure and magnetocaloric effect were investigated using backscatter scanning electron microscopy, X-ray diffraction, differential scanning calorimetry and phys- ical property measurement system. When the plate was annealed at 1373 K, rl phase was formed by a solid-state peritectoid reaction. A first-order magnetic phase transition occurred in the vicinity of 188 K, and the effective refrigeration capacities reached 203.5J/kg and 209.7J/kg in plates annealed for I h and 3 h, respectively, under a magnetic field change of 3T. It is suggested that centrifugal casting may become a new approach to prepare high-performance La-Fe-Si magnetocaloric plates for prac- tical applications, which could largely accelerate the formation of rl phase during high-temperature heat-treatment process due to refined and homogeneous honeycombed microstructure.

关键词： La-Fe-Si Magnetocaloric effect Rapid solidification Centrifugal casting Phase transition

Hydrodynamic Interactions of Three Barges in Close Proximity in A Floatover Installation

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China Ocean Engineering 2016年第3期30卷 343-358页

作者：许鑫李欣杨建民肖龙飞 state Key Laboratory of Ocean Engineering Shanghai Jiao Tong University

The hydrodynamics of side-by-side barges are much more complex than those of a single barge in waves because of wave shielding, viscous effects and water resonance in the gap. In the present study, hydrodynamic coefficients in the frequency domain were calculated for both the system of multiple bodies and the isolated body using both low-order and higher-order boundary-element methods with different element numbers. In these calculations, the damping-lid method was used to modify the free-surface boundary conditions in the gap and to make the hydrodynamic results more reasonable. Then far-field, mid-field and near-field methods were used to calculate wave-drift forces for both the multi-body system and the isolated body. The results show that the higher-order method has faster convergence speed than the low-order method for the multi-body case. Comparison of different methods of computing drift force showed that mid-field and far-field methods have better convergence than the near-field method. In addition, corresponding model tests were performed in the Deepwater Offshore Basin at Shanghai Jiao Tong university. Comparison between numerical and experimental results showed good agreement.

关键词： multi-body side-by-side hydrodynamic interaction floatover