La1/3Sr2/3Fe1-xCoxO3体系中的Co替代效应研究

本文通过对La1/3Sr2/3Fe1-xCoxO3系列样品进行X射线衍射(XRD)和变温电阻率(p～T)、比热(C～T)、磁化率(M～T)等测试,研究了Co掺杂对该系列样品的晶体结构和电热磁性质的影响.结果表明,随着Co掺杂量的增加,晶胞体积单调减小;电阻中电荷有序(charge ordering,CO)的特征逐渐消失.Co含量低的样品随着温度降低发生顺磁-反铁磁(PM-AFM)转变和金属-绝缘体(M-I)转变;Co含量高的样品则在磁转变温度以下表现出团簇玻璃型短程铁磁有序行为,并且在整个测量温区内具有金属导电特性.这些证明Co掺杂引起电子的局域化效应是导致体系电磁和输运行为发生变化的主要原因.     

Dynamical properties of a stochastic predator-prey model with functional response

A stochastic prey-predator model with functional response is investigated in this paper. A complete threshold analysis of coexistence and extinction is obtained. Moreover, we point out that the stochastic predator-prey model undergoes a stochastic Hopf bifurcation from the viewpoint of numerical simulations. Some numerical simulations are carried out to support our results.     

An incremental bundle method for portfolio selection problem under second-order stochastic dominance

Numerical Algorithms - We propose a preconditioner to accelerate the convergence of the GMRES iterative method for solving the system of linear equations obtained from discretize-then-optimize...     

链式多智能体遗传算法在分布式电源全时序上优化配置

分布式电源的选址与定容是微电网研究所面临的重要问题,本文主要考虑规划地区的24-h负荷时序特性和气候特点的24-h负荷变换的情况下的DG优化配置。针对以上问题,通过链式多智能体遗传算法对其进行优化处理。首先通过算法对IEEE33节点系统进行测试,验证算法在分布式电源优化配置中的优越性,并对PG E69节点配电网进行24-h时序的全过程模拟仿真优化,结果验证了多智能体遗传算法能在分布式电源配置上的有效性,同时提高微电网接入的预测精度,加快收敛速度,改进陷入局部最优的可能性等问题,对微电网在规划选址与定容选择上提供工程参考的实用性。     

Transmission-mode GaN photocathode based on graded Al_xGa_(1-x)N buffer layer

We create a GaN photocathode based on graded Alx Ga1-x N buffer layers to overcome the influence of buffer-emission layer interface on the photoemission of transmission-mode GaN photocathodes.A gateshaped spectral response with a 260-nm starting wavelength and a 375-nm cut-off wavelength is obtained.Average quantum efficiency is 15% and short wavelength responses are almost equivalent to long wavelength ones.The fitted interface recombination velocity is 5×104 cm/s,with negligible magnitude,proving that the design of the graded buffer layers is efficient in obtaining good interface quality between the buffer and the emission layer.     

Effects of locally resonant modes on underwater sound absorption in viscoelastic materials

Recently, by introducing locally resonant scatterers with spherical shape proposed in phononic crystals into design of underwater sound absorption materials, the low-frequency underwater sound absorption phenomenon induced by the localized resonances is observed. To reveal this absorption mechanism, the effect of the locally resonant mode on underwater sound absorption should be studied. In this paper, the finite element method, which is testified efficiently by comparing the calculation results with those of the layer multiple scattering method, is introduced to investigate the dynamic modes and the corresponding sound absorption of localized resonance. The relationship between the resonance modes described with the displacement contours of one unit cell and the corresponding absorption spectra is discussed in detail, which shows that the localized resonance leads to the absorption peak, and the mode conversion from longitudinal to transverse waves at the second absorption peak is more efficient than that at the first one. Finally, to show the modeling capability of FEM and investigate shape effects of locally resonant scatterers on underwater sound absorption, the absorption properties of viscoelastic materials containing locally resonant scatterers with ellipsoidal shape are discussed.     

GaAs1-xPx中混晶无序与Fe深中心的性质

对不同组分的掺FeⅢ-Ⅴ族混晶GaAs1-xPx,测量了Fe深受主中心空穴热发射的非指数恒温暗电容瞬态及DLTS谱。用混晶无序使Fe深能级展宽的模型理论拟合实验结果,得到Fe能级Gauss型展宽的半宽和中心能级的热发射率,并确定出基态空穴跃迁的中心能级的焓变与组分的关系:先是减少,而后增大,与由光电容方法得到的Gibbs自由能变量与组分x的关系明显不同。 进一步讨论表明,上述两种测量方法得到的Fe中心的激活能不同,可能反映Fe中心的键合状态和混晶无序诱导的品格弛豫的影响。     

单向耦合映象格子的时空混沌同步

以耦合映象格子为对象,研究了时空混沌系统的同步问题. 基于Lyapunov稳定性定理,通过恰当地选择驱动函数,实现了两个单向耦合映象格子的完全同步. 仿真模拟验证了这种同步方法的有效性. 讨论了控制参量对同步速率的影响. 仿真模拟还表明,在存在系统偏差并受到噪声影响的情况下,仍然可以实现两系统的同步,这种同步方法具有一定的抗干扰能力. 关键词： 时空混沌 同步 耦合映象格子     

直接冷却的高温超导磁体热稳定性有限元仿真

制冷机直接冷却超导磁体是一门新兴技术,研究超导磁体在直接冷却下的热稳定性具有重要意义。用有限元方法解决复杂边界问题的热力学问题非常有效,而有限元分析软件ANSYS能使得用有限元法解决问题更加方便。该文用有限元方法对直接冷却高温超导磁体进行了热稳定性数值仿真。仿真结果表明,在设定热负荷作用下,直接冷却的B i2223系高温超导磁体具有较好的热稳定性,磁体温度低于其临界温度。