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Synthesis of aluminum nitride nano-powder by decomposed diethylaluminum azide in aerosols

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Journal of University of Science and Technology Beijing 2004年第5期11卷 428-432页

作者： YapingYe lihuaWang WeilanQian MuTang YanbingWu appliedscienceschool UniversityofScienceandTechnologyBeijingBeijing100083China

An aerosol process for making aluminum nitride nano-powder by decompositionof single compound diethylalumimm az-ide was described. X-ray diffraction (XRD) and transmissionelectron microscopy (TEM) were used to study characters of the A1N powder. It is shown that theprocess can produce spherical A1N powder with mean particle diameters ranging from 10 to 50 nm at500-800°C. The generated amorphous A1N powder is characterized by a BET (Brunauer-Emmett-Teller)surface area of 103 m2/g and is very reactive to moisture.

关键词： aluminum nitride aerosol reactor nanometric diethylaluminun azide

Robust exponential control of a class of systems with uncertainties

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Journal of University of Science and Technology Beijing 2002年第2期9卷 149-155页

作者： FuchengLiao TohruKATAYAMA 等 DepartmentofMathematicsandMechanics AppliedScienceSchooluniversityofScienceandTechnologyBeijingBeijing100083China DepartmentofAppliedMathematicsandPhysics GraduateSchoolofInfor

The robust exponential stabilization problem for uncertain systems isstudied. Based on the solution for a nominal linear quadratic regulator problem with a prescribeddegree of stability, the methods of constructing state feedback controllers are developed to ensurethe robust stability of the closed loop system under the conditions weaker than the matchingcondition. Also, the cases where the matching condition is satisfied are considered in detail. Someexamples are included to show the solution methods.

关键词： robust control exponential control uncertain system matching condition

Theoretical Analysis of Lattice Parameter Effect on Order-Disorder Transformation Based on Pair Potential

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Journal of University of Science and Technology Beijing 2002年第1期9卷 53-58页

作者： TimotheeNsongo XiaodongNi StateKeyLaboratoryforAdvancedMetalsandMaterials.UniversityofScienceandTechnologyBeijing Beijing100083China appliedscienceschool UniversityofScienceandTechnologyBeijingBeijing1

Based on pair potential, the Bragg Williams (B-W) model is modified to takeinto account the effect of the lattice parameter on theoretical order-disorder transformationanalysis. The main purpose of this work is to understand the basic aspects of this effect andrelated reasonable model on order-disorder transformation. In the present approach, theconfiguration free energy is chosen as function of the lattice parameter and the long-range *** energy is calculated through Taylor's expansion, starting from the disordered state. It wasfound that the configuration free energy has been strongly modified when the lattice parameter istaken into account. It was also found only one type of order-disorder transformation exists in ABalloy and three kinds of order-disorder transformations for non-equiatomic alloy system such as A_3Balloy. This result is in agreement with experiments.

关键词： order-disorder transformation computer simulation pair potential phasetransformation

Frequency-dependent dynamic effective properties of porous materials

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Journal of University of Science and Technology Beijing 2005年第3期12卷 236-242页

作者： PeijunWei ZhupingHuang appliedscienceschool UniversityofSciencesandTechnologyBeijingBeijing100083China DepartmentofMechanicsandEngineeringSciences PekingUniversityBeijing100080China

The frequency-dependent dynamic effective properties (phase velocity, attenuation and elastic modulus) of porous materials are studied numerically. The coherent plane longitudinal and shear wave equations, which are obtained by averaging on the multiple scattering fields, are used to evaluate the frequency-dependent dynamic effective properties of a porous material. It is found that the prediction of the dynamic effective properties includes the size effects of voids which are not included in most prediction of the traditional static effective properties. The prediction of the dynamic effective elastic modulus at a relatively low frequency range is compared with that of the traditional static effective elastic modulus, and the dynamic effective elastic modulus is found to be very close to the Hashin-Shtrikman upper bound.

关键词： dynamic effective properties porous material size effects multiple scattering

Performance of a combined capacitor based on ultrafine nickel oxide/carbon nanotubes composite electrodes

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Journal of University of Science and Technology Beijing 2004年第6期11卷 533-538页

作者： XiaofengWang YanqiuCao YiqiangLu QiqianSha JiLiang appliedscienceschool UniversityofScienceandTechnologyBeijingBeijing100083China DepartmentofMechanicalEngineering TsinghuaUniversityBeijing100084China

A new sol-gel process for the preparation of ultrafine nickel hydroxideelectrode materials was developed. The composite electrodes consisting of carbon nanotubes andNi(OH)_2 were developed by mixing the hydroxide and carbon nanotubes together in different massratios. In order to enhance energy density, a combined type pseudocapacitor/electric double layercapacitor was considered and its electrochemical properties were characterized by cyclic voltammetryand dc charge/discharge test. The combined capacitor shows excellent capacitor behavior with anoperating voltage up to 1.6 V in KOH aqueous electrolyte. Stable charge/discharge behaviors wereobserved with much higher specific capacitance values of 24 F/g compared with that of EDLC (12 F/g)by introducing 60 percent Ni(0H)_2 in the anode material. By using the modified anode of aNi(OH)_2/carbon nanotubes composite electrode, the specific capacitance of the cell was lesssensitive to discharge current density compared with that of the capacitor employing pure nickelhydroxide as anode. The combined capacitor in this study exhibits high energy density and stablepower characteristics.

关键词： nickel oxide carbon nanotubes combined capacitor supercapacitor

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Journal of University of Science and Technology Beijing 2002年第2期9卷 104-106页

作者： LiancunZheng XinxinZhang 等 appliedscienceschool universityofScienceandTechnologyBeijingBeijing100083China MechanicalEngineeringSchool UniversityofScienceandTechnologyBeijingBeijing100083China

A suitable similarity transformation is introduced to reduce the laminarboundary layer equations of power law fluids to a class of singular nonlinear two-point boundaryvalue problems. The kin friction and shear stress distributions for boundary layer flow over amoving flat plate are investigated by utilizing the shooting technique. Results indicate that foreach fixed value of the power law exponent n or the velocity ratio parameter xi, the skin frictionand shear stress decrease with the increasing of n or xi respectively.

关键词： boundary layer skin friction similarity solution shooting technique

Free boundary value problems for a class of generalized diffusion equation

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Journal of University of Science and Technology Beijing 2002年第6期9卷 422-425页

作者： LiancunZheng XinxinZhang 等 appliedscienceschool UniversityofScienceandTechnologyBeijingBeijing100083China MechanicalEngineeringSchool UniversityofScienceandTechnologyBeijingBeijing100083China

The transport behavior of free boundary value problems for a class ofgeneralized diffusion equations was studied. Suitable similarity transformations were used toconvert the problems into a class of singular nonlinear two-point boundary value problems andsimilarity solutions were numerical presented for different representations of heat conductionfunction, convection function, heat flux function, and power law parameters by utilizing theshooting technique. The results revealed the flux transfer mechanism and the character as well asthe effects of parameters on the solutions.

关键词： free boundary value problem generalized diffusion equation nonlinearboundary problem shooting technique

Surface-particle-emulsion heat transfer model between fluidized bed and horizontal immersed tube

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Journal of University of Science and Technology Beijing 2002年第2期9卷 99-103页

作者： PingWu XuFeng 等 appliedscienceschool universityofScienceandTechnologyBeijingBeijing100083China MechanicalEngineering SchooluniversityofScienceandTechnologyBeijingBeijing100083China

A mathematical model, surface-particle-emulsion heat transfer model, ispresented by considering voidage variance in emulsion in the vicinity of an immersed surface. Heattransfer near the surface is treated by dispersed particles touching the surface and through theemulsion when the distance from the surface is greater than the diameter of a particle. A film withan adjustable thickness which separates particles from the surface is not introduced in this *** coverage ratio of particles on the surface is calculated by a stochastic model of particlepacking density on a surface. By comparison of theoretical solutions with experimental data fromsome references, the mathematical model shows better qualitative and quantitative prediction forlocal heat transfer coefficients around a horizontal immersed tube in a fluidized bed.

关键词： fluidized bed heat transfer two-phase flow mathematical model

Temperature distribution and control in liquefied petroleum gas fluidized beds

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Journal of University of Science and Technology Beijing 2004年第3期11卷 202-206页

作者： LiWang PingWu YanpingZhang JingYang LigeTong MechanicalEngineeringSchool UniversityofScienceandTechnologyBeijingBeijing100083China appliedscienceschool UniversityofScienceandTechnologyBeijingBeijing100083China

Temperature distribution and control have been investigated in a liquefiedpetroleum gas (LPG) fluidized bed with hollow corundum spheres (A1_2O_3) of 0.867-1.212 mm indiameter at moderately high temperatures (800-1100℃). Experiments were carried out for the airconsumption coefficient α in the range of 0.3 to 1.0 and the fluidization number N in the range of1.3 to 3.0. Particle properties, initial bed height, α and N all affect temperature distribution inthe bed. Bed temperature can be adjusted about 200℃ by combined the adjusting of α and N.

关键词： liquefied petroleum gas fluidized bed temperature distribution