平行线偏光激发CPT共振方案实验研究

目前的相干布居囚禁(CPT)原子钟和CPT磁场计中普遍采用圆偏振光方案 (σ⁺-σ⁺)实现CPT共振, 该方案对原子的利用率较低. 为了提高原子的利用率, 本文实验研究了通过平行线偏振相干双色光与⁸⁷Rb原子作用实现CPT共振的方案(lin//lin). 与σ⁺-σ⁺方案相比较, lin//lin方案消除了极化暗态, 获得更多工作原子. 在相同的实验条件下, 开展对比实验研究获得了信噪比为σ⁺-σ⁺方案2倍, 微分线型信号的中心斜率为σ⁺-σ⁺方案1.65倍的CPT共振信号. 研究结果表明该方案是实现低功耗原子钟、磁场计等设备的理想候选.     

尖晶石型LiMn2O4晶体结构及锂离子筛H+/Li+交换性质研究

采用密度泛函理论平面波超软赝势和广义梯度近似法对尖晶石型LiMn2O4及其锂离子筛HMn2O4的晶体结构和性质进行了从头计算。PW91泛函最为有效,Li+被H+取代后HMn2O4晶胞收缩,点阵常数从LiMn2O4的0.823 nm减小至0.799 nm,其XRD峰也相应向高角度方向明显位移。经同种格点原子的XRD分析表明,Mn、O两元素对XRD方式和强度起着决定作用。其中Li呈+1价完全离子化,可被H+彻底交换,H与周围O在等电子密度图中呈现电子云相互连接,只带有0.42个正电荷。价轨道分态密度表明,Mn-O之间强的共价键合主要归因于Mn-d和O-p在费米能级下-7.3~-1.6 eV间的轨道重叠,形成了有利于H+/Li+交换的骨架空穴隧道。阵点和空穴多面体的体积遵守如下顺序:V8a>V48f>V8b、V16c>V16d、V16c>V48f。Li+最易迁移至邻近的16c位置,碱金属离子的交换受到离子半径和作用能大小的限制。     

Analysis of the power law logistic population model with slowly varying coefficients

We apply a multiscale method to construct general analytic approximations for the solution of a power law logistic model, where the model parameters vary slowly in time. Such approximations are a useful alternative to numerical solutions and are applicable to a range of parameter values. We consider two situations—positive growth rates, when the population tends to a slowly varying limiting state; and negative growth rates, where the population tends to zero in infinite time. The behavior of the population when a transition between these situations occurs is also considered. These approximations are shown to give excellent agreement with the numerical solutions of test cases. Copyright © 2012 John Wiley & Sons, Ltd.     

吸烟者调查抽样设计案例研究

本文通过对南宁市烟草公司拟进行的吸烟者调查抽样设计案例的研究,讨论了有限总体概率抽样原理和技术方面某些问题的具体应用。其中包括:抽样单位的选择;总体总值的单位均值估计量和比估计量;总体比率的比估计量;直接写出比估计量方差的法则,等等。在此基础上,进行了案例实证分析。     

具有反馈控制的单种群对数模型稳定性

研究具有反馈控制的单种群对数模型．通过构造适当的Lyapunov函数．我们让得系统的正平衡点是无条件全局稳定的．所得结果补充和完善了已有的结果．     

The comparison between Homotopy Analysis Method and Optimal Homotopy Asymptotic Method for nonlinear age-structured population models

This paper presents comparison between Homotopy Analysis Method (HAM) and Optimal Homotopy Asymptotic Method (OHAM) for the solution of nonlinear age-structured population models. Three examples have been presented to illustrate and compare these methods. In OHAM the convergence region can be easily adjusted and controlled. Comparison between our solution and the exact solution shows that the both methods are effective and accurate in solving nonlinear age-structured population models with HAM being the more accurate for the same number of terms. It was also found that OHAM require more CPU time.     

周向重叠三分螺旋折流板换热器壳侧性能试验研究

对倾斜角为20°、24°、28°和32°的单头以及32°的双头周向重叠三分螺旋折流板换热器和弓形折流板换热器的传热和压降性能进行了测试,换热器采用公共壳体和可更换管芯结构。采用壳侧轴向雷诺数和轴向欧拉数分别作为反映壳侧流量和阻力系数的无因次参数。试验结果显示在试验范围内周向重叠三分螺旋折流板换热器壳侧换热系数、壳侧压降和综合性能指标都随着倾斜角增大而减小;倾斜角20°方案的性能指标最佳,其平均壳侧努塞尔数和轴向欧拉数与弓形折流板方案的数值之比分别为1.123和0.45;双头螺旋折流板方案的换热系数和压降都大于同样倾斜角的单头螺旋折流板方案,但两者的综合性能较接近。     

基于ADL模型的贵州人口时间序列分析

众所周知,经济对人口总量有显著性影响。本文分析了人口总量关于出生率、死亡率和GDP的Granger成因,最后用自回归分布滞后模型研究贵州省人口模型,得到精度约为8‰的贵州人口的自回归分布滞后模型。     

Well‐posedness of a nonlinear evolution equation arising in growing cell population

We prove that a nonlinear evolution equation which comes from a model of an age‐structured cell population endowed with general reproduction laws is well‐posed. Copyright © 2011 John Wiley & Sons, Ltd.