The work function of hydrothermally synthesized UO2 and the implications for semiconductor device fabrication

The photoelectric work function of nearly stoichiometric (111) and (100) hydrothermally grown UO₂ was measured to be 6.28 ± 0.36 eV and 5.80 ± 0.36 eV, respectively. Candidate metals for electrical contacts are identified for both rectifying and non‐rectifying contacts based on work function, lattice compatibility, and electrical conductivity.     

Harmonic operation of high gain harmonic generation free electron laser

In high gain harmonic generation (HGHG) free electron laser (FEL), with the right choice of parameters of the modulator undulator, the dispersive section and the seed laser, one may make the spatial bunching of the electron beam density distribution correspond to one of the harmonic frequencies of the radiator radiation, instead of the fundamental frequency of the radiator radiation in conventional HGHG, thus the radiator undulator is in harmonic operation (HO) mode. In this paper, we investigate HO of HGHG FEL.Theoretical analyses with universal method are derived and numerical simulations in ultraviolet and deep ultraviolet spectral regions are given. It shows that the power of the 3rd harmonic radiation in the HO of HGHG may be as high as 18.5% of the fundamental power level. Thus HO of HGHG FEL may obtain short wavelength by using lower beam energy.     

用于高热流密度器件冷却的热管散热器实验研究

针对大型计算机服务器CPU的耗能量,探讨了一种新的热管排布方式的散热器,并对其散热性能进行了实验研究.研究结果表明,采用此种热管散热器,最高热流密度为74.3W/cm2,其冷却风速控制在4m/s即可满足芯片冷却要求.同时根据模拟计算得到的散热器底板温度分布,可有助于对热管排布方式的优化设计.     

Study on the denoising method for the electromagnetic ultrasonic echoes from multiple interfaces

The electromagnetic ultrasound is used in the detection of interfaces of the adhesive multilayer structures to solve the unstable coupling problem in ultrasonic testing by traditional piezoelectric transducers. Based on the analysis of the transforming mechanism of electromag-netic ultrasound energy and the resultant dead zone from mutual inductance of the transducer, the wavelet filtering by soft-thresholding and adaptive noise canceling methods are used simul-taneously to the detected electromagnetic ultrasonic signals to overcome the drawbacks of the low signal to noise ratio （SNR） and the wide intrinsic dead zone of the transducer. Processed results in the interface detection of a three layered adhesive sample of steel and rubber materials demonstrate that the wavelet filtering enhances the SNR about 12dB while the adaptive noise canceling narrows the dead zone effectively.     

气源MBE外延自组装GeSi量子点光致荧光研究

利用气源分子束外延设备（MBE）制作了GeSi自组装量子点样品。利用原子力显微镜（AFM）和光致荧光（PL）光谱研究了量子点的形貌和光学性质。气源MBE在较低温度下生长的量子点材料具有较高的量子点覆盖度。200K以下载流子以局域激子形式束缚在量子点中,激子束缚能约为17meV。升温至200K,载流子的输运过程发生变化。对量子点PL积分强度与温度关系曲线进行拟合得到量子点中空穴跃迁至浸润层的热激活能为129meV。     

Robust Preparation of Atomic Concatenated Greenberger–Horne–Zeilinger States via Shortcuts to Adiabaticity

Here, a protocol for robust preparation of an atomic concatenated Greenberger–Horne–Zeilinger (C‐GHZ) state via shortcuts to adiabaticity (STA) is proposed. The devices for implementing the protocol consist of atoms, cavities, and the optical fibers, which are feasible with current technology. The atoms are trapped in the separated cavities allowing individual control over each atom with classical fields. STA helps to design Rabi frequencies of classical fields so that the atoms can be driven from the initial states to the target states. The numerical simulations show that the protocol holds robustness against atomic spontaneous emissions and photonic leakages. Thus, the protocol may be realized by experiments in the near future.     

On Estimation of Temperature Uncertainty Using the Second Order Adjoint Problem

The uncertainty of temperature prediction from the heat flux error is estimated using first and second order adjoint equations. The adjoint codes developed for the inverse heat transfer problems provide the uncertainty estimation for the corresponding forward problems. Numerical tests corroborate the feasibility of fast uncertainty estimation using Hessian maximum eigenvalue obtained via second order adjoint equations.     

Turbulence Closure with a Topography-parameter-free Single Equation Model

A new topography-parameter-free turbulence closure, based on a transport equation for the pseudo eddy viscosity, is described. The model is tested against experimental data of several flow cases across the Mach number range and compared to Menter's single equation model and to the Spalart-Allmaras model. The main conclusion is that the new closure outperforms the other two models in both low and high speed flows.     

Dislocation-density-based constitutive modelling of tensile flow and work-hardening behaviour of P92 steel

The flow and work-hardening behaviour of tempered martensitic P92 steel have been investigated using phenomenological constitutive model in the temperature range 300–873 K for the strain rates ranging from 3.16 × 10^?5 to 1.26 × 10^?3 s^?1. The analysis indicated that the hybrid model reduced to Estrin–Mecking (E–M) one-internal-variable model at intermediate and high temperatures. Further, the analysis also indicated that dislocation dense martensite lath/cell boundaries and precipitates together act as effective barriers to dislocation glide in P92 steel. The flow behaviour of the steel was adequately described by the E–M approach for the range of temperatures and strain rates examined. Three distinct temperature regimes have been obtained for the variations in work-hardening parameters with respect to temperature and strain rate. Signatures of dynamic strain ageing in terms of the anomalous variations in work-hardening parameters at intermediate temperatures and the dominance of dynamic recovery at high temperatures have been observed. The evaluation of activation energy suggested that deformation is controlled by the dominance of cross-slip of dislocations at room and intermediate temperatures, and climb of dislocations at high temperatures.     

利用蝴蝶型纳米结构下的极化门方案输出单个阿秒脉冲

理论研究了在蝴蝶型纳米结构下运用多周期极化门方案驱动He原子输出高次谐波以及阿秒脉冲的特点.结果表明,由于纳米结构表面的等离子共振增强现象,谐波截止能量得到延伸.同时,由于激光场呈现空间非均匀性,长量子路径对谐波的贡献被减弱.并且,在极化门控制下,谐波平台区的贡献只来源于单一的谐波辐射能量峰,进而形成一个147 eV的超长平台区.最后,通过叠加平台区的谐波,可获得一个持续时间在30 as的超短脉冲.