Visible light absorption of (Fe,C/N) co-doped NaTaO_3: DFT+U

The effects of Fe–C/N co-doping on the electronic and optical properties of NaTaO_3 are studied with density functional theory. Our calculations indicate that mono-doped and co-doped sodium tantalate are both thermodynamically stable.The co-doping sodium tantalate can reduce the energy band gap to a greater degree due to the synergistic effects of Fe and C(N) atoms than mono-doping sodium tantalate, and has a larger optical absorption of the whole visible spectrum. The band alignments for the doped NaTaO_3 are well positioned for the feasibility of hydrogen production by water splitting. The Fe–C co-doping can enhance the absorption of the visible light and its photocatalytic activity more than Fe–N co-doping due to the different locations of impurity energy levels originating from their p–d hybridization effect.     

Stable Intrinsic Long Range Antiferromagnetic Coupling in Dilutely V Doped Chalcopyrite

A stable and long-range antiferromagnetic(AFM) coupling without charge carrier mediators has been searched for a long time,but the existence of this kind of coupling is still lacking.Based on first principle calculations,we systematically study carrier free long-range AFM coupling in four transition metal chalcopyrite systems:ABTe₂(A=Cu or Ag,B=Ga or In) in the dilute doping case.The AFM coupling is mainly due to the p-d coupling and electron redistribution along the interacting chain...     

Muon radiography technology for detecting high-Z materials

This paper studies the possibility of using the scattering of cosmic muons to identify threatening high-Z materials. Various scenarios of threat material detection are simulated with the Geant4 toolkit. PoCA （Point of Closest Approach） algorithm reconstructing muon track gives 3D radiography images of the target material. Z-discrimination capability, effects of the placement of high-Z materials, shielding materials inside the cargo, and spatial resolution of position sensitive detector for muon radiography are carefully studied. Our results show that a detector position resolution of 50 μm is good enough for shielded materials detection.     

粒子加速器局部控制网形变分析

基于泰勒展开的方法实现局部控制网的拟合,使用卡方检验判断局部控制网中是否存在形变点。若存在形变点,则在选权迭代的过程中找到局部控制网中所有的形变点,并将卡方检验通过作为迭代终止条件。对哈尔滨工业大学空间地面模拟装置2号终端控制网的两期观测成果进行了分析,实验表明,将卡方检验和选权迭代法加入控制网拟合之后,可以很好地探测出局部控制网中的形变点。在找出所有形变点之后,可以求得更为准确的局部控制网拟合参数。     

Structural, elastic, phonon and electronic properties of a MnPd alloy

The structural, elastic, phonon and electronic properties of a MnPd alloy have been investigated using the first-principles calculation. The calculated lattice constants and electronic structure agree well with the experimental results. The microscopic mechanism of the diffusionless martensitic transition from the paramagnetic B2 (PM-B2) phase to the antiferromagnetic L10 (AFM-L10) phase through the intermediate paramagnetic L10 (PM-L10 ) phase has been explored theoretically. The obtained negative shear modulus C′= (C11-C12)/2 of the PM-B2 phase is closely related to the instability of the cubic B2 phase with respect to the tetragonal distortions. The calculated phonon dispersions for the PM-L10 and AFM-L10 phases indicate that they are dynamically stable. However, the AFM-L10 phase is energetically most favorable according to the calculated total energy order, so the PM-L10 →AFM-L10 transition is caused by the magnetism rather than the electron-phonon interaction. Additionally, the AFM-L10 state is stabilized through the formation of a pseudo gap located at the Fermi level. The calculated results show that the CuAu-I type structure in the collinear antiferromagnetic state is dynamically and mechanically stable, thus is the low temperature phase.     

第一性原理计算MAlH4(M=Na,K)的结构和弹性性质

基于密度泛函理论研究并比较了两种储氢材料NaAlH₄和KAlH₄的晶格参数,弹性性质和电子结构.计算结果表明NaAlH₄和KAlH₄都是绝缘体,Al—H之间是共价键,M(M=Na,K)与AlH₄之间是离子键.NaAlH₄和KAlH₄的弹性常数都比较小而且NaAlH₄的弹性常数要大于KAlH₄的弹性常数,对此给予了解释. 关键词： 配位金属氢化物 电子结构 弹性性质     

高通量下GEM探测器高压供电模式研究

GEM探测器的供电一般采用电阻链分压供电模式和多路分立供电模式,在低通量X射线下测量时区别不大,但是在高通量X射线时,电阻链分压供电模式会带来饱和效应引起工作电压的变化,造成探测器工作不稳定。本研究在高通量X 射线照射下,研究了有效面积为100 mm100 mm三层级联GEM探测器的有效增益(稳定性) 与不同高压供电模式的关系。通过测量不同分压电阻值(1, 2, 5 到30 MΩ)的实验研究,发现随着X 射线通量的增加,在电阻链分压供电模式下,出现了GEM探测器感应电极的读出电流饱和趋势,分析了可能导致饱和效应出现的原因。结果表明,当入射X射线在探测器上的有效吸收剂量不断增加时,电阻链供电模式需要调整分压单元电阻值,或者采用多路分立供电模式,从而避免因饱和效应引起的GEM探测器有效增益的变化,实现探测器稳定的工作状态。There are two methods of the HV power supply for the GEM detector. One is a HV channel divided by the resistive chain and the other is the several separate HV channels. In the smaller dose rate of X-ray, all of the methods are similar. When the dose rate increases, the resistive chain-dividing mode has more obvious saturation effect and the working voltage of the GEM detector is unstable. In the paper, a GEM detector with an effective area of 100 mm100 mm has been studied in the high dose rate using X-tube. The unit values in the divider resistance chain are set to 1, 2, 5 and 30 MΩ respectively in the test. With the resistive chain-dividing mode, the readout current of the GEM detector’s anode tends to saturate when the dose rate of X-ray increases,and the reasons of the saturation effect are analyzed. The results indicate that the effective absorbed dose of X-ray by the triple GEMs detector reaches to the pecific value and the divider resistance needs to re-select, even the several separate HV channels mode should be considered. It will keep the constant of the working voltage of the GEM detector without the saturation effect and gain variation and the performance of GEM detector is stable.     

4He闪烁裂变中子探测器的中子灵敏度

对4He闪烁裂变中子探测器的中子灵敏度进行了理论和实验研究。采用蒙特卡罗方法模拟了不同能量中子和不同厚度裂变靶产生的裂变碎片在4He中的能量沉积,计算结果表明:中子在4He气中的能量沉积曲线和裂变碎片的能量沉积曲线能够互补,从而使探测器对中子的能量响应变得更平坦;探测器的中子灵敏度为10-15 Ccm2量级。并对探测器的中子灵敏度进行了实验标定,实验结果与理论计算结果较为一致。     

紧紧抓住“任意一点”或点“滑动”的条件巧解填空选择题

在有些数学题目中,常有某些一般交待性的条件不为同学们所重视,如"任意一点"或点在某线上"滑动",若能从中挖掘出题目隐藏的含意,就可以迅速简捷地解决问题,下面通过几个例子加以说明.