低铂Pt/SiC制备及对氧还原反应的催化性能表征

采用乙二醇回流法成功制备了理论含铂量为14;的Pt/SiC阴极催化剂.利用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)、X射线光电子能谱(XPS)对催化剂晶型结构、表面形貌和表面电子结构进行了表征.应用循环伏安法和旋转圆盘电极进行电化学测试,研究了Pt/SiC催化剂对氧还原反应催化活性.结果表明,在180℃条件下合成的Pt/SiC催化剂的平均粒径为3.4 nm,Pt是面心立方结构.Pt在SiC表面以0价为主,有利于O2在其表面的吸附和解离.Pt/SiC-180催化剂具有与商业Pt/C(20;)催化剂相近的氧还原催化性能.Pt/SiC-180催化剂的起始还原电位为0.95 V,氧还原过程以4-电子路径为主,且稳定性和抗甲醇中毒性能明显优于商业Pt/C催化剂.优良的催化性能和较低的含铂量使其有望成为低铂燃料电池阴极催化潜在材料.     

Enhancement of next-nearest-neighbouring entanglement in quantum Ising spin chain

Using the method of the Jordan--Wigner transformation for solving different spin--spin correlation functions, we have investigated the generation of next-nearest-neighbouring entanglement in a one-dimensional quantum Ising spin chain with the Gaussian distribution impurities of exchange couplings and external magnetic fields taken into account. The maximal value of entanglement between the next-nearest-neighbouring qubits in the transverse Ising model was analysed in detail by varying the effectively controlled parameters such as interchange coupling, magnetic field and the system impurity. For such systems, where both exchange couplings and external magnetic field disorder appear, we show that it is possible to achieve next-nearest-neighbouring entanglement better than the previously discussed pure Ising spin chain case. We also show that the Gaussian distribution impurity can induce next-nearest-neighbouring entanglement, which can be used as a means to characterize quantum phase transition.     

Comments on <Emphasis Type="Italic">Three-point explicit compact difference scheme with arbitrary order of accuracy and its application in CFD</Emphasis>

The explicit compact difference scheme, proposed in Three-point explicit compact difference scheme with arbitrary order of accuracy and its application in CFD by Lin et al., published in Applied Mathematics and Mechanics （English Edition）, 2007, 28（7）, 943-953, has the same performance as the conventional finite difference schemes. It is just another expression of the conventional finite difference schemes. The proposed expression does not have the advantages of a compact difference scheme. Nonetheless, we can more easily obtain and implement compared with the conventional expression in which the coefficients can only be obtained by solving equations, especially for higher accurate schemes.     

Entropy of field interacting with two two-qubit atoms

We use quantum field entropy to measure the degree of entanglement for a coherent state light field interacting with two atoms that are initially in an arbitrary two-qubit state. The influence of different mean photon number of the coherent field on the entropy of the field is discussed in detail when the two atoms are initially in one superposition state of the Bell states. The results show that the mean photon number of the light field can regulate the quantum entanglement between the atoms and light field.     

K-ε-T model of dense liquid-solid two-phase turbulent flow and its application to the pipe flow

To predict the characteristics of dense liquid-solid two-phase flow, K-ε-T model is established, in which the turbulent flow of fluid phase is described with fluid turbulent kinetic energy K_f and its dissipation rate ε_f, and the particles random motion is described with particle turbulent energy K_p and its dissipation rate ε_p and pseudothermal temperature T_p. The governing equations are also derived. With K-ε-T model, numerical study of dense liquid-solid two-phase turbulent up-flow in a pipe is performed. The calculated results are in good agreement with experimental data of Alajbegovic et al. (1994), and some flow features are captured.     

Al－Mn合金镀层的组成结构及其耐蚀性

研究了在低温熔盐中（低于２００℃）电沉积Ａｌ－Ｍｎ合金镀层成分的控制,镀层化学组成与结构之间的关系以及镀层的耐蚀性能．提出影响镀层锰含量的主要因素是熔盐中锰离子的浓度．镀层含锰量在２５～４０（ｗｔ）％之间可形成非晶态结构．实验表明,Ａｌ－Ｍｎ合金镀层在０．５ｍｏｌ／ＬＨ＿２ＳＯ＿４熔液及ＮａＣｌ溶液中具有优良的耐蚀性,非晶态结构的Ａｌ－Ｍｎ合金镀层的耐蚀性更为优异．     

Entanglement properties in a system of a pairwise entangled state

Based on the quantum information theory, this paper has investigated the entanglement properties of a system which is composed of the two entangled two-level atoms interacting with the two-mode entangled coherent fields. The influences of the strength of light field and the two parameters of entanglement between the two-mode fields on the field entropy and on the negative eigenvalues of partial transposition of density matrix are discussed by using numerical calculations. The result shows that the entanglement properties in a system of a pairwise entangled states can be controlled by appropriately choosing the two parameters of entanglement between the two-mode entangled coherent fields and the strength of two light fields respectively.     

高效的基于傅里叶单像素成像的亚像素级边缘检测技术

针对无法实现先验的边缘检测场景,并解决边缘提取效率过低的问题,提出一种更高效的基于傅里叶单像素成像的亚像素级边缘检测方法。该方法结合快速傅里叶单像素成像,减少图像算法的相移步数,在原有四步相移的基础上分别实现了三步相移与两步相移边缘检测。该算法上的改进能够在同等采样数下扩大参与边缘提取的频谱宽度,从而提升边缘提取效率。数值仿真结果表明,与四步相移亚像素级边缘检测相比,无噪声条件下两步相移在655~13 100次左右的采样数区间内峰值信噪比增长幅度高出2.27 dB,噪声条件下低于0.054噪声浮动比率时两步相移方法可以获得比四步相移更高的边缘提取质量。该方法可以一定程度上提升边缘提取效率,同时促进单像素成像领域与图像处理方向的技术交叉和应用化发展。     

Ca(OH)2/CaO热化学储能过程中变孔隙率影响的多物理场耦合数值模拟研究

基于Ca(OH)₂/CaO的热化学储能体系在实验中均表现出孔隙结构的显著变化，而该现象在已有的大多数数值模拟研究中并未被考虑。本文针对该现象建立了变孔隙率反应动力学模型及非稳态“流动–传热–化学反应”耦合模型，并基于此对直接、间接传热式固定床反应器中Ca(OH)₂/CaO的定/变孔隙率脱水反应过程特征参数(反应渗透率、压力、温度、反应速率及转化率等)变化进行了对比模拟研究。结果表明：定孔隙率模型与变孔隙率模型之间有明显的差异，且变孔隙率模型更能体现实际反应过程的特征。以初始孔隙率为0.8的工况为例，定孔隙率假设在直接传热式反应器中的转化速率比变孔隙率模型快19.8%，而在间接传热式反应器中转化速率比变孔隙率慢6.1%。说明以往研究中使用的定孔隙率假设高估了直接传热式反应器的性能，而低估了间接传热式反应器的性能。     

超奈奎斯特相干光传输系统载波频偏估计算法

提出一种基于训练序列相位差+调频Z变换（CZT）的两级频偏估计算法。该方案采用设计的时域训练序列块并结合块内和块间多次平均平滑噪声影响，以较低开销实现频偏的稳定粗估计，并进一步基于第一级频偏粗估计设定第二级CZT估计范围，以较低计算复杂度完成最终高精度频偏估计。三载波128 GBaud偏振复用十六进制正交幅度调制（PM-16QAM）超奈奎斯特（FTN）波分复用（WDM）系统的仿真结果表明，加速因子为0.95、0.90、0.85时，所提算法训练开销仅为1.56%，即可实现-8～8 GHz范围内的稳定频偏估计，残余频偏分别为2、2.5、3 MHz左右。与估计精度基本相当的传统盲四次方FFT频偏估计算法相比，所提算法的总体计算复杂度显著降低，约为传统算法的8%。