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Vanadium-Doped Semi-Insulating 6h-SiC for Microwave Power Device Applications

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Journal of Materials Science & Technology 2009年第1期25卷 102-104页

作者： Liana Ning Zhihong feng Yingmin Wang Kai Zhang Zhen feng State Key Laboratory of Crystal Materials Shandong University Jinan 250100 hebei Semiconductor Research Institute Shijiazhuang 050051 China

Two-inch semi-insulating SiC bulk crystals with resistivity higher than 1 × 10^6 Qcm were achieved by vanadium doping during sublimation. Secondary-ion-mass-spectrometry （SIMS） was employed to determine the concentration of impurities in the crystals, such as B, AI, V and N. These results indicated that the concentration of nitrogen and aluminum kept on decreasing and the concentration of B and V was almost constant during the whole growth. An inner crucible was used to control the exhausting of vanadium, which made the uniformity of the high resistivity （〉1×10^6 Ωcm） in the wafer up to 80%. high-performance AlGaN/GaN high-electronmobility-transistor （hEMT） materials and devices were grown and fabricated on semi-insulating 6h-SiC sub- strates. The two-dimensional electron gas （2DEG） mobility at room-temperature was 1795 cm^2/V-s. The charge carrier concentration of the substrate determined by capacitance-voltage （C-V） test was 7.3×10^15 cm^-3. The device with a gate width of I mm exhibits a maximum output power of 5.5 W at 8 Ghz, which proves the semi-insulating property of the substrates indirectly.

关键词： Silicon Carbide Semi-insulating Vanadium-doped AlGaN/GaN hEMT

STUDIES OF LOW-CONCENTRATION ChROMATE PASSIVE FILM FOR ZINC-BASED ALLOY COATED STEEL WIRES

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Acta Metallurgica Sinica(English Letters) 1999年第5期12卷 736-738页

作者： Li, Y. Wang, h.R. feng, F.L. Wei, X.J. Northeastern Univ Shenyang China

The corrosion resistance of a low concentration chromate passive film for zinc based alloy coated steel wires was assessed by salt spray and electrochemical corrosion tests. XPS and AES analyses showed that the comp... 详细信息

关键词： chromate passive film zinc based alloy coating XPS AES

A UNIFORM CONVERGENT PETROV-GALERKIN METhOD FOR A CLASS OF TURNING POINT PROBLEMS

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Journal of Computational Mathematics 2024年第5期42卷 1356-1379页

作者： Li feng Zhongyi huang Department of Mathematical Sciences Tsinghua UniversityBeijing 100084China

In this paper,we propose a numerical method for turning point problems in one dimension based on Petrov-Galerkin finite element method(PGFEM).We first give a priori estimate for the turning point problem with a single boundary turning *** we use PGFEM to solve it,where test functions are the solutions to piecewise approximate dual *** prove that our method has a first-order convergence rate in both L∞h norm and a discrete energy norm when we select the exact solutions to dual problems as test *** results show that our scheme is efficient for turning point problems with different types of singularities,and the convergency coincides with our theoretical results.

关键词： Turning point problem Petrov-Galerkin finite element method Uniform convergency

A Special Kind of Interplanetary Coronal Mass Ejection

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Research in Astronomy and Astrophysics 2024年第12期24卷 185-193页

作者： h.Q.feng Y.Zhao G.Q.Zhao h.B.Li L.Xiang J.M.Wang Institute of Space Physics Luoyang Normal University henan Key Laboratory of Electromagnetic Transformation and Detection Luoyang Normal University

It is generally believed that coronal mass ejections(CMEs) have magnetic flux rope structures because of their helical shapes. however, only about 30%–40% of interplanetary CMEs(ICMEs) have a local magnetic flux rope structure. The usual explanations are that the spacecraft only crossed the flank of the ropes and failed to detect the complete magnetic flux rope structure or that some processes destroyed these magnetic flux rope structures. Several studies suggest that some ICMEs inherently possess disordered magnetic fields and consequently exhibit no magnetic flux-rope structures. We introduce a special kind of ICME which has a low magnetic field magnitude and stable magnetic field direction, relatively fast expansion speed, and lower proton temperature and density. All three of the measured magnetic field components are relatively stable. We want to know whether these ICMEs also have magnetic flux rope structures or not. We identified 20 special ICMEs and analyzed their evolution based on their observed characteristics. We took a special ICME as an example, which had an apparent rope configuration at 1 au but evolved to a special ICME at 5.4 au, to illustrate that this kind of ICME could come from magnetic clouds(MCs) whose rope structure had been being stretched due to expansion. We inferred that the missing obvious flux rope structure may be due to the expansion of MCs, not the flank crossing effect. however, more than 50% of the events were associated with the dominant x-component of the magnetic field, which indicates a leg ***, the detection of part of these special ICMEs may also be the result of the leg-crossing effect.

关键词： (Sun:) solar wind interplanetary medium Sun: coronal mass ejections (CMEs)

Marcinkiewicz integrals with rough kernels in h^(1)(s^(n-1))

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Frontiers of Mathematics in China 2021年第4期16卷 1163-1189页

作者： Daiqing ZhANG feng LIU School of Computer Science and Mathematics Fujian University of TechnologyFuzhou 350118China Shandong University of Science and Technology Qingdao 266590China

This paper is devoted to studying the Marcinkiewicz integral operators associated to polynomial compound *** new bounds for the above operators on the Lebesgue,Triebel-Lizorkin,and Besov spaces are established by assuming that their rough kernels are given byΩ∈h^(1)(s^(n-1))and h∈Δ_(γ)(R_(+))for someγ>*** should be pointed out that the bounds are independent of h,Ω,γ,and the coefficients of the polynomials in the definition of the operators.

关键词： Marcinkiewicz integral polynomial curve h^(1)(s^(n-1)) Triebel-Lizorkin space

Effects of Exogenous Silicon on Photosynthetic Capacity and Antioxidant Enzyme Activities in Chloroplast of Cucumber Seedlings Under Excess Manganese

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Agricultural Sciences in China 2009年第1期8卷 40-50页

作者： feng Jian-peng ShI Qing-hua WANG Xiu-feng College of horticultural Science and Engineering Shandong Agricultural University Tai＇an 271018 P.R.China State Key Laboratory of Crop Biology Tai＇an 271018 P.R.China

Effects of silicon on photosynthetic parameters and antioxidant enzymes of chloroplast in cucumber seedlings under excess Mn were studied. Compared with the control, excess Mn significantly inhibited net photosynthetic rate （Pn）, stomatal conductance, as well as the maximum yield of the photosystem II photochemical reactions （Fv/Fm） and the quantum yield of photosysytem II electron transport （Φ PSII）, application of Si reversed the negative effects of excess Mn. In the further investigation, it was obtained that application of Si significantly increased the activities of enzymes related with ascorbate-glutathione cycle including ascorbate peroxidase （APX）, dehydroascorbate reductase （DhAR） and glutathione reductase （GR） in cucumber chloroplast under excess Mn, this could be responsible for the lower accumulation of h2O2 and lower lipid peroxidation of chloroplast induced by Mn, and resulted in keeping higher photosynthesis.

关键词： cucumber excess manganese photosynthesis chlorophyll fluorescence chloroplast antioxidant enzymes

Ab initio Study on Structures and Isomerization of Magnesium Fluorosilylenoid h2SiFMgF

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Chinese Journal of Chemical Physics 2008年第6期21卷 541-546页

作者： Yi-jian Zhang Mei-jiang Li Guo-qiao Lai Da-cheng feng Sheng-yu feng Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education Hangzhou Normal University Hangzhou 310012 China School of Chemistry and Chemical Engineering Shandong University Ji'nan 250100 China

The structures and isomerization of magnesium fluorosilylenoid h2SiFMgF were investigated by ab initio molecular orbital theory. Four equilibrium structures and three isomeric transition states were located and fully optimized at the B3LYP/6-31G（d,p） and G3MP2B3 levels, respectively. Based on the B3LYP/6- 31G（d,p） optimized geometries, harmonic frequencies of various structures were obtained and 29Si chemical shifts were calculated. The solvent effects were investigated by means of the polarizable continuum model using ThF as a solvent at B3LYP/6-31G（d,p） level. Isomerization paths for isomers were confirmed by intrinsic reaction coordinate calculations. The calculated results show that tetrahedral structure has the lowest energy and is the most stable; tetrahedral, three-membered ring, and p-complex structures are suggested to be the experimentally detectable ones; and a-complex structure has the highest energy and will not exist.

关键词： Magnesium fluorosilylenoid Ab initio calculation B3LYP/6-31G(d p) theory Isomerization

Microstructure and Strain hardening of a Friction Stir Welded high-Strength Al–Zn–Mg Alloy

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Acta Metallurgica Sinica(English Letters) 2014年第4期27卷 723-729页

作者： A.h.feng D.L.Chen Z.Y.Ma W.Y.Ma R.J.Song School of Materials Science and Engineering Tongji University State Key Laboratory of Advanced Welding Production Technology School of Materials Science and EngineeringHarbin Institute of Technology Department of Mechanical and Industrial Engineering Ryerson UniversityTorontoON M5B 2K3Canada Shenyang National Laboratory for Materials Science Institute of Metal ResearchChinese Academy of Sciences

Microstructural evolution and strain hardening behavior of a friction stir welded（FSWed） high-strength7075Al-T651 alloy were *** nugget zone was observed to consist of fine and equiaxed recrystallized grains with a low dislocation density and free of original precipitates,but containing uniformly distributed *** strength,joint efficiency,and ductility of the FSWed joints increased with increasing welding speed.A joint efficiency of ＊91% was achieved at a welding speed of 400 mm/min and rotational rate of 800 r/min,while the ductility remained basically the same as that of the base *** was no obvious strain rate sensitivity observed in both base metal and welded *** both the base metal and FSWed joints exhibited stage III and IV hardening characteristics,the hardening capacity,strain hardening exponent,and strain hardening rate all increased after friction stir welding.

关键词： Aluminum alloy Friction stir welding Mechanical properties Strain hardening

Comparative study of two lattice Boltzmann multiphase models for simulating wetting phenomena: implementing static contact angles based on the geometric formulation

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Applied Mathematics and Mechanics(English Edition) 2018年第4期39卷 513-528页

作者： feng YE Qinfeng DI Wenchang WANG feng ChEN huijuan ChEN Shuai hUA Shanghai Institute of Applied Mathematics and Mechanics Shanghai University Shanghai Key Laboratory of Mechanics in Energy Engineering Shanghai University

Wetting phenomena are widespread in nature and industrial applications. In general, systems concerning wetting phenomena are typical multicomponent/multiphase complex fluid systems. Simulating the behavior of such systems is important to both scientific research and practical applications. It is challenging due to the complexity of the phenomena and difficulties in choosing an appropriate numerical method. To provide some detailed guidelines for selecting a suitable multiphase lattice Boltzmann model, two kinds of lattice Boltzmann multiphase models, the modified S-C model and the h-C-Z model, are used in this paper to investigate the static contact angle on solid surfaces with different wettability combined with the geometric formulation(Ding, h. and Spelt, P.D. M. Wetting condition in diffuse interface simulations of contact line motion. Physical Review E, 75(4), 046708(2007)). The specific characteristics and computational performance of these two lattice Boltzmann method(LBM) multiphase models are analyzed including relationship between surface tension and the control parameters, the achievable range of the static contact angle, the maximum magnitude of the spurious currents(MMSC), and most importantly, the convergence rate of the two models on simulating the static contact angle. The results show that a wide range of static contact angles from wetting to non-wetting can be realized for both models. MMSC mainly depends on the surface tension. With the numerical parameters used in this work, the maximum magnitudes of the spurious currents of the two models are on the same order of magnitude. MMSC of the S-C model is universally larger than that of the h-C-Z model. The convergence rate of the S-C model is much faster than that of the h-C-Z model. The major foci in this work are the frequently-omitted important details in simulating wetting phenomena. Thus, the major findings in this work can provide suggestions for simulating wetting phenomena with LBM multiphase

关键词： lattice Boltzmann method(LBM) wetting phenomenon static contact angle