带喷流超声速后台阶流场精细结构及其运动特性研究

采用基于纳米示踪的平面激光散射技术(NPLS)对带超声速喷流的后台阶流动精细结构进行了研究. 来流马赫数为3.4, 喷流实测马赫数为2.45, 而名义马赫数为2.5. 结果清晰地揭示了激波、剪切层、混合层、Kelvin-Helmholtz涡、羊角涡及湍流大尺度结构等大量典型流场结构. 基于大量流场精细结构图像, 对典型位置处的结构进行了空间两点相关性分析, 在喷流混合层前端涡结构小于湍流充分发展的尾端, 结构角相对也小. 喷流工作时, 模型台阶下游表面由一薄层气膜覆盖. 获得了模型流向和不同高度展向平面内的流场结构, 对照纹影试验结果, 分析了流动特点及时间演化规律. 采用微型压力扫描系统测试了模型表面的压力系数分布, 靠近喷流下游处压力系数区域0.0146. 针对NPLS图像做了流动的分形维数的分析, 发现在流动初始阶段分形维数接近于1, 越靠下游分形维数越高.     

Effects of pressure and/or magnetism on superconductivity of δ-MoN single crystal

Effects of pressure and/or magnetism on the critical superconducting temperature(Tc)ofδ-Mo N single crystal were investigated using a Maglab system.Theδ-Mo N single crystal was synthesized at extreme conditions of high pressure and high temperature.The carrier density ofδ-Mo N single crystal as a function of applied pressure was determined using Hall coefficient measurement.     

First-principles study of structure and nonlinear optical properties of CdHg(SCN)4 crystal

The geometric structure,electronic structure,and optical properties of CdHg(SCN)4 crystal are calculated by using the density functional perturbation theory and Green function screening Coulomb interaction approximation.The band gap of CdHg(SCN)4 crystal is calculated to be 3.198 eV,which is in good agreement with the experimental value 3.265 eV.The calculated second-order nonlinear optical coefficients are d_(14) = 1.2906 pm/V and d_(15) = 5.0928 pm/V,which are in agreement with the experimental results(d_(14)=(1.4 ±0.6) pm/V and d_(15)=(6.0 ±0.9) pm/V).Moreover,it is found that the contribution to the valence band mainly comes from Cd-4d,Hg-5d states,and the contributions to the valence band top and the conduction band bottom predominantly come from C-2p,N-2p,and S-3p states.The second-order nonlinear optical effect of CdHg(SCN)_4 crystal results mainly from the internal electronic transition of(SCN)~-.     

Baseline optimization of SQUID gradiometer for magnetocardiography

SQUID gradiometer techniques are widely used in noise cancellation for biomagnetic measurements.An appropriate gradiometer baseline is very important for the biomagnetic detection with high performance.By placing several magnetometers at different heights along the vertical direction,we could simultaneously obtain the synthetic gradiometers with different baselines.By using the traditional signal-to-noise ratio(SNR) as a performance index,we successfully obtain an optimal baseline for the magnetocardiography(MCG) measurement in a magnetically shielded room(MSR).Finally,we obtain an optimal baseline of 7 cm and use it for the practical MCG measurement in our MSR.The SNR about 38 dB is obtained in the recorded MCG signal.     

二氧化碳对质子化甲醇的溶剂化作用 (cited: 1)

利用团簇模型研究了二氧化碳对质子化甲醇的溶剂化作用．H⁺(CH₃OH)(CO₂)_n⁺(n=1～7)的量子化学计算结果表明,需要3个或4个二氧化碳分子完成甲醇的羟基第一溶剂层．除了氢键,二氧化碳分子间的相互作用对大团簇的稳定性也起到了重要的作用．在这些溶剂化作用的早期阶段,不容易发生质子从甲醇到二氧化碳的转移过程．模拟的红外光谱揭示了自由O-H伸缩振动、氢键作用后的O-H伸缩振动、以及二氧化碳的O-C-O伸缩振动频率是研究质子化甲醇溶剂化过程的灵敏探针．     

硅磁微粒/聚苯胺复合物的制备及其对染料废水的吸附-降解性能

通过水热法制备碳微球、共沉淀法制备空心Zn Fe2O4和原位聚合法制备Zn Fe2O4/Si O2/PANI复合物,并表征其结构、形貌、组成和性质.结果表明,Si O2对铁氧体的包覆能提高二元复合物对染料废水的降解性能;铁氧体与二氧化硅物质的量比(nZn Fe2O4/nSi O2)为1:3的Zn Fe2O4/Si O2复合物对染料废水具有较好的降解作用;Zn Fe2O4/Si O2/PANI复合物对染料废水的光催化降解活性随苯胺质量分数(wAn)的增加而增大,当wAn为50%时,Zn Fe2O4/Si O2/PANI复合物对染料废水去除率高达98%.样品因具有磁性而回收方便,重复使用性能良好.     

A statistical model of microcracking of concrete under uniaxial compression

At increasing external load, numerous microcracks propagate in discrete and successive stages within a body of concrete material according to the hierarchy of their tensile fracture strengths. Each microcrack propagation is conditional upon the statistical encounter of its associated fracture criterion. This paper shows the development of a statistical model for the progressive microcrack growth process within a body of concrete material at monotonic uniaxial loading in compression to ultimate failure. This model is formulated by using the Weibull's statistical theory of the strength of materials. The body of heterogeneous concrete material is simulated as a continuum comprising a large population of microscopic “weakest-link” isoenergy elements, each of which contains a unit-volume of representative micro-structural material which is linearly elastic, homogeneous and isotropic. The statistical modelling is derived from the stochastic evaluation of the tensile micro-fracture probabilities of these isoenergy elements at increasing global uniaxial compressive strains.     

Fast reversible electron transfer for photosynthetic reaction center from wild type Rhodobacter sphaeroides re-constituted in polycation sandwiched monolayer film

Direct reversible electron transfer for photosynthetic reaction center from wild type Rhodobacter sphaeroides re-constituted in polycation sandwiched monolayer film was observed in this work. The redox potential E0' = 0.46 V vs. NHE for first primary donor redox couple P/P+ was accurately measured from reversible CV or SWV peaks, which were quite close to those obtained from optic redox titration method. Reaction center (RC) in film was found re-constituted in such an ordered way that the orientation of RC favored the electron transfer in film. Thus, the protein electroactivity seems to be turned on in this artificial biomimic thin film. Furthermore, RC in the film features a photo-induced redox-peak fluctuation, suggesting an intact and functional state for RC in such film. Redox peaks were also found dependent of pH, implying a proton-coupled electron transfer occurring in film. Charge recombination was observed accompanied with change of electrochemical driving force. Electrochemical model assuming several classes of electroactive sites in the films on the electrode with a dispersion of standard potentials successfully fits SWV experimental data at different pulse height and frequency.     

Structural,electrical and optical properties of SnO2 films deposited on Y-stabilized ZrO2 (1 0 0) substrates by MOCVD

SnO₂ films have been deposited on Y-stabilized ZrO₂ (YSZ) (1 0 0) substrates at different substrate temperatures (500–800 °C) by metalorganic chemical vapor deposition (MOCVD). Structural, electrical and optical properties of the films have been investigated. The films deposited at 500 and 600 °C are epitaxial SnO₂ films with orthorhombic columbite structure, and the HRTEM analysis shows a clear epitaxial relationship of columbite SnO₂(1 0 0)||YSZ(1 0 0). The films deposited at 700 and 800 °C have mixed-phase structures of rutile and columbite SnO₂. The carrier concentration of the films is in the range from 1.15×10¹⁹ to 2.68×10¹⁹ cm⁻³, and the resistivity is from 2.48×10⁻² to 1.16×10⁻² Ω cm. The absolute average transmittance of the films in the visible range exceeds 90%. The band gap of the obtained SnO₂ films is about 3.75–3.87 eV.