70 GHz二次谐波倍频回旋速调管研究

 对70 GHz二次谐波倍频回旋速调管高频结构和电子与波互作用进行了研究。研究了TE02模腔体绕射品质因数及模式转化，解决了二次谐波倍频回旋速调管漂移段不能截止70 GHz的TE01模而引起的腔体间高频串扰的问题。分析了注电流、输入功率、电子横纵速度比和电子注引导中心半径等参数对输出功率、增益和效率的影响。针对二次谐波回旋速调管放大器工作频带窄、效率低，进行了高频结构优化设计，显著地展宽了工作频带，提高了互作用效率。在理论分析和高频计算的基础上，建立了注-波互作用PIC（粒子模拟）模型，进行了粒子模拟计算和优化，得到了70 GHz 的二次谐波倍频四腔回旋速调管放大器设计方案。粒子模拟结果表明：在工作电压70 kV，注电流13 A，电子注横向速度与纵向速度比为1.5时，中心频率69.81 GHz输出功率256 kW，带宽160 MHz，电子效率28%，饱和增益大于44 dB。     

Molecular dynamics of MgSiO3 perovskite melting

The melting curve of MgSiO分子动力学 MgSiO3钙钛矿 熔化温度 高压melting temperature, molecular dynamics, high pressureProject supported by the National Natural Science Foundation of China (Grant Nos 10274055 and 10376021),the Natural Science Foundation of Gansu Province, China (Grant No 3ZS051-A25-027) and the Scientific Research Foundation of Education Bureau of Gansu Province, China (Grant No 0410-01).2005-01-125/8/2005 12:00:00 AMThe melting curve of MgSiO3 perovskite is simulated using molecular dynamics simulations method at high pressure. It is shown that the simulated equation of state of MgSiO3 perovskite is very successful in reproducing accurately the experimental data. The pressure dependence of the simulated melting temperature of MgSiO3 perovskite reproduces the stability of the orthorhombic perovskite phase up to high pressure of 130GPa at ambient temperature, consistent with the theoretical data of the other calculations. It is shown that its transformation to the cubic phase and melting at high pressure and high temperature are in agreement with recent experiments.     

Surface reconstructions of InGaAs alloys

The surface reconstructions of In_xGa_1−xAs alloys grown by molecular beam epitaxy on the (0 0 1) surfaces of GaAs and InAs have been studied by reflection high-energy electron diffraction and scanning tunnelling microscopy. A surface phase diagram is presented for the nominally strain-free alloy as a function of substrate temperature and alloy composition, and structural models for the commonly observed 3× reconstructions are discussed. Two new, electronically stable structural models are described that account for the transition of the In_xGa_1−xAs surface alloy from a c(4 × 4) to an asymmetric 3× reconstruction and that are fully consistent with all current experimental evidence.     

基于液晶调制器调制的实时测温系统

分析了一种基于基尔霍夫定律的钽酸锂(LiTaO3)热释电探测器作为接收元件的实时测温系统中,机械式调制盘对测量精度影响,提出了改变机械式调制盘对测量精度的影响的方法;介绍了液晶调制器的结构、对辐射调制的原理以及在使用过程中的优点。设计了利用液晶调制器替代机械调制器的钽酸锂热释电实时测温系统。结果表明,利用液晶调制器改进后的测温系统在给定的温度范围中,测量精度均有明显的改善,符合测量要求。     

Nd:LuVO_4晶体的拉曼光谱研究

采用不同的几何配置测量了Nd:LuVO4晶体的室温拉曼光谱,根据群论对称性分类计算了该晶体的红外和拉曼活性振动模并与实验结果做了比较,指认了测定的特征谱线。测量并分析了Nd:LuVO4晶体A1g全对称类的高温拉曼光谱,讨论了拉曼频移随温度变化的关系,认为晶体的热膨胀是引起拉曼频移变化的主要原因。     

金属冲击温度的辐射法测量问题

 金属的冲击温度及熔化温度测量对构建其完全状态方程具有重要意义。简要综述了用于金属冲击温度及熔化温度辐射法测量的一维热传导理想界面模型和非理想界面模型，并着重对模型中明示或隐含的关键假定的合理性、影响金属冲击温度与熔化温度结果的主要因素进行了分析、讨论，以期对实验数据有一个合理的评估。还讨论了求解理想和非理想界面模型一维热传导方程界面温度时所隐含的冲击压缩下热导率不随温度而变、冲击压缩下金属样品/窗口界面辐射的灰体假定，以及窗口材料的透明性、非理想界面模型中表观界面温度的修正、动载条件下金属高压熔化温度的测量、界面的非Flourier热传导等问题。分析结果表明，目前采用辐射法测量大致可以得到冲击温度，在发生熔化的情况下可获得熔化温度，但离精密测量的要求还有较大差距。     

手分为多节段的人体热调节模型研究

将人体热调节柱状模型和手的多节段模型结合起来,建立了更完整的人体热调节模型。利用有限元方法对人体热调节数学模型进行了数值求解,并设计试验证明了模型的正确性。结果表明: (1)当取合适的血流量时,实验值和计算值的变化趋势一致,且手部温度稳定时,血流量都在确定的范围内;(2)血液流量是手部温度场变化的主要因素,人体组织和动脉入口温度对手部温度影响较小。     

Structural studies of Cr-doped mullite derived from single-phase precursors

Cr-doped mullites were prepared from single-phase precursors containing up to 9.60 wt% Cr₂O₃ using a sol-gel technique followed by thermal treatment. Particle induced X-ray emission spectroscopy and X-ray powder diffraction were used to characterize the samples. Mullites were orthorhombic, space group Pbam. Cr doping caused the increase of unit-cell parameters. Strongest expansion was noticed along c-axis followed by a and b (Δc/c=0.089, Δa/a=0.061, Δb/b=0.045% per mole Cr₂O₃). A second phase, namely θ-(Al,Cr)₂O₃, was revealed by XRD in the sample containing 9.60 wt% Cr₂O₃. The structure of mullites was refined by the Rietveld method, location of Cr³⁺ was performed by the EPR spectroscopy. At low chromium doping level (Cr₂O₃ content less than ∼5 wt%) Cr³⁺ ions were substituted for Al³⁺ in the AlO₆ octahedra of the mullite structure (M1 site). For higher doping level, Cr³⁺ ions were additionally substituted for Al³⁺ in the AlO₆ octahedra of the second phase [θ-(Al,Cr)₂O₃ at 1400 °C, or α-(Al,Cr)₂O₃ at 1600 °C] which segregated in the system. Substitution of Cr³⁺ for Al³⁺ on M1 site in the mullite structure resulted in increase of average distances in (M1)O₆ octahedron and decrease of average distances in T*O₄ tetrahedron, while average distances in TO₄ tetrahedron stayed almost constant.     

二分量高温超导机理

用两种电子态,讨论了金属—绝缘相变、反铁磁性—金属相变,以及相分离、正常态—超导态相变、非费米液体行为、高Tc等 关键词： 两种电子态 格林函数 玻色化 高温超导     

微型热驱动热声热机热端换热器的优化设计

该文基于热声环境,采用厘米级扁管和deltaE数值计算对微型热声换热器进行了优化设计。