Effects of hydrostatic pressure on Raman scattering in Ge quantum dot superlattices

Self-organized Ge/Si quantum dots (QD's) in strained Si/Ge short-period superlattices are studied by Raman scattering under hydrostatic pressure excited in-resonance and off-resonance with the confined Ge-like E₁ transition of Ge using 488 and 514.5 nm lines from an argon-ion laser and 632.8 nm line from a He-Ne laser. The Raman spectra of Ge-Ge, Si-Ge and Si-2TA modes of the QD's were obtained as a function of pressure in the range of 1-70 kbar. Our results show that the mode Grüneisen parameter of the Ge-Ge phonon mode in QD's is found to be γ=0.81±0.01, which is smaller than that of the bulk Ge. We observe resonance effects with the confined Ge-like E₁ transition and the pressure coefficient of this resonating electronic transition obtained is ∼5±1 meV kbar⁻¹.     

Magnetic Resonance Imaging of fluidized beds

This paper reviews recent developments in Magnetic Resonance Imaging (MRI) which enable it to follow particle motion in fluidized beds. Imaging with a spatial resolution of 400 μm and a temporal resolution of 1 ms is now feasible; particle velocities of order 1 m/s can be measured with good accuracy. The technique provides voidage fractions on a motion-picture basis and particle velocity fields. Limitations are: (i) the particles must contain appropriate atoms e.g. C or H; and (ii) currently the fluidized bed diameter cannot exceed 50 mm, though measurements from larger units will doubtless become available. MR studies on fluidized beds are described: results are reported for (i) air jets entering the bed (ii) bubbling and slugging beds and (iii) dispersion in a bubbling bed. The data are consistent with published measurements. Study (i) helps to resolve the longstanding puzzle about the behaviour of an air jet entering a fluidized or partly-fluidized bed, answering the question: does the entering air form bubbles or a continuous jet?     

交流传动HXD1电力机车谐振原因分析与对策

多台HXD1交流传动电力机车在太原铁路局湖东机务段同时运行时,发生了牵引网和机车变流器谐振现象,致使机车跳闸保护不能正常工作,严重影响了列车调度运行。铁道部专门组织了现场测试。本文对测试结果进行了理论分析分析,找出了谐振的原因,提出了可能的解决办法,并给出了最经济的解决办法。解决的办法被采纳后HXD1机车与牵引网的谐振问题不再发生。     

电磁驱动的金属泵结构设计和工作原理分析

设计电磁驱动的金属泵机械结构,分析其振动机理,确定其输出功率的影响因素,比较金属泵和压电泵的优缺点。     

一种5.8 GHz磁控管谐振系统的模拟分析

利用HFSS结合等效电路对一种18叶片5.8 GHz磁控管的谐振系统进行了冷态模拟与分析,利用Master/Slave边界条件对磁控管谐振腔模型进行了改进,对叶片端部尺寸对磁控管谐振系统的影响进行了分析,分析结果与实验结果相吻合。为磁控管谐振系统的设计提供了依据。     

自振荡电子镇流器的设计方法

该文提出并分析了利用自振荡指令电路的电子镇流器的设计方法.作为继电控制系统的自振荡电子镇流器,为确定其参数,应用了(等效频率传输的)描述函数及扩展的Nyquist稳定性判据.提供了40 W荧光灯用电子镇流器的模拟与试验结果,以证实该设计方法的可行性和有效性.     

Flame-vortex interaction and mixing behaviors of turbulent non-premixed jet flames under acoustic forcing

This study examines the effect of acoustic excitation using forced coaxial air on the flame characteristics of turbulent hydrogen non-premixed flames. A resonance frequency was selected to acoustically excite the coaxial air jet due to its ability to effectively amplify the acoustic amplitude and reduce flame length and NO_x emissions. Acoustic excitation causes the flame length to decrease by 15% and consequently, a 25% reduction in EINO_x is achieved, compared to coaxial air flames without acoustic excitation at the same coaxial air to fuel velocity ratio. Moreover, acoustic excitation induces periodical fluctuation of the coaxial air velocity, thus resulting in slight fluctuation of the fuel velocity. From phase-lock PIV and OH PLIF measurement, the local flow properties at the flame surface were investigated under acoustic forcing. During flame-vortex interaction in the near field region, the entrainment velocity and the flame surface area increased locally near the vortex. This increase in flame surface area and entrainment velocity is believed to be a crucial factor in reducing flame length and NO_x emission in coaxial jet flames with acoustic excitation. Local flame extinction occurred frequently when subjected to an excessive strain rate, indicating that intense mass transfer of fuel and air occurs radially inward at the flame surface.     

轮式装载机行驶中仰俯振动的分析及处理

轮式装载机因真轴距铰短,在行驶中易产生仰俯振动,故将影响其行驶平顺性和行驶速度的提高。本文对轮式装载机在行驶中的俯仰振动问题进行分析,得出控制其俯仰振动的有关参数,为设计时采取必要的技术措施提供理论依据。     

车用涡轮增压器压气机叶轮振动特性分析

利用CAD软件对增压器的压气机叶轮进行了三维实体造型,并运用有限元分析软件I-DEAS对叶轮进行振动特性分析,得到了叶轮在不同转速下的固有频率值及相应振型,通过Matlab软件绘制Camp-bell图,找到了叶轮容易发生共振时的转速和激振频率.从而为该增压器叶轮的优化设计提供依据.     

MRI研究泠冻馒头微波复热过程水分的迁移变化

普通新鲜馒头在-18℃的环境中冷冻24h后，取出进行微波解冻加热实验。利用核磁共振成像（MRI）技术研究冷冻馒头复热过程中水分的迁移变化。馒头在受热过程中水分的损失直接影响馒头的品质。实验比较了冷冻馒头在微波蒸碗不加水和加水两种方式下含水量的变化，发现微波蒸碗加水复热对馒头的水分有一定的补偿效果。