An efficient Fréchet differentiable high breakdown multivariate location and dispersion estimator

A good robust functional should, if possible, be efficient at the model, smooth, and have a high breakdown point. M-estimators can be made efficient and Fréchet differentiable by choosing appropriate ψ-functions but they have a breakdown point of at most 1/(p + 1) in p dimensions. On the other hand, the local smoothness of known high breakdown functionals has not been investigated. It is known that Rousseeuw's minimum volume ellipsoid estimator is not differentiable and that S-estimators based on smooth functions force a trade-off between efficiency and breakdown point. However, by using a two-step M-estimator based on the minimum volume ellipsoid we show that it is possible to obtain a highly efficient, Fréchet differentiable estimator whilst still retaining the breakdown point. This result is extended to smooth S-estimators.     

A Polarization-Stabilized Fiber-Optical Output Infrared Laser Source

In this paper, we successfully invented a polarization controlled light source for coherent or noncoherent fiber communication systems. The structure of our experiment includes 89C51 control board and feedback circuit which can stabilize states of polarization (SOPs) of output light. From the SOP modulation results, the given degree of polarization can be effectively controlled and the polarization state can be arbitrarily changed.     

用有限解析差分格式数值求解化学输运方程

本文用有限解析差分格式研究在多孔介质中化学输运问题的数值模型,系统地计算结果表明:1.有限解析差分格式能够消除数值弥散和伪振荡; 2.随着弥散数(Peclct数)的减小(增加),浓度突破曲线将延迟到达和形状变陡,最终趋近浓度对流曲线;3.当流速数增加后,非稳态吸附对浓度分布的影响趋近稳态吸附的影响。     

Numerical simulation of the flow field in a reactor for titanium dioxide production

A physicochemical and fluid dynamic model is formulated for the numerical simulation of the flow field in a reactor for titanium dioxide production, the turbulence motion is described by theKε equation, the governing equations are solved by the SIMPLER algorithm devised by Partankar and Spalding. The velocity, tmperature and concentration fields are obtained for three cases: A) with chemical reaction and thermal insulation on the walls; B) with chemical reaction and wall temperature is 450K; C) without chemical reaction and thermal insulation on the walls, and the physicochemical numerical simulation for the titanium dioxide production has been done. The results of the paper can be used as a theoretical guide for the engineers in the design of such reactors.     

Two-dimensional adaptive Eulerian-Lagrangian method for mass transport with spatial velocity distribution

A Eulerian-Lagrangian scheme is used to solve the two-dimensional advection-dispersion equation. Concentration and its partial differential operator are decomposed into advection and dispersion terms. Thus, advection is formally decoupled from dispersion and solved by continuous forward particle tracking. Dispersion is handled by implicit finite elements on a fixed Eulerian grid. Translation of steep gradients of concentration in advection-dominated flow regimes, is done without numerical distortion. Continuous spatial distribution of velocities are evaluated by using Galerkin's approach in conjunction with Darcy's law based on hydraulic input data from each element. The method was implemented on coarse FE grid with linear shape functions, demonstrating no over/under shooting and practically no numerical dispersion. Simulations, covering a wide range of Peclet numbers, yield high agreement with analytic and practical results.     

Impacts of higher-order dispersions and saturable nonlinearities on modulation instability in negative-refractive metamaterials

On the basis of the standard linear stability analysis and Drude electromagnetic model,the impacts of higher-order dispersions and three kinds of typical saturable nonlinearities on modulation instability(MI) have been analyzed and calculated for negative-refractive metamaterials(MMs).Our results show that the MI gain spectra consist of only one spectral region instead of one or two regions in ordinary materials,which may be close to or far from the zero point.Particularly,the spectrum far from the zero point has a high cut-off frequency but a narrow spectral width,which is obviously beneficial to the generation of high-repetition-rate pulse trains.Moreover,MI characteristics here will vary with the normalized angular frequency which can be modified by adjusting the structures of negative-refractive MMs,signifying the controllability of bistable solitons and MI based applications.The effects of saturable nonlinearities are similar to those in ordinary materials.     

异核碱金属原子间的三体相互作用系数

利用碱金属原子的模型势和稳定变分法,首次计算了异核碱金属原子间的三体相互作用系数.为了说明计算结果的精度,同时计算了碱金属原子的电多级极化率.与其他作者的理论数据和有关实验数据的比较表明,本文所得到的异核碱金属原子间的三体相互作用系数是可靠的.     

色散补偿光子晶体光纤结构参数对其色散的影响

光子晶体光纤由于其灵活可调的色散特性用作色散补偿具有极大的应用潜力. 设计了一种色散补偿光子晶体光纤, 并运用频域有限差分法模拟了其色散特性,从理论上分析了其结构参数孔间距Λ和空气占空比d/Λ对该光子晶体光纤的色散系数的影响, 并且实际制备出了3种不同结构参数的光子晶体光纤. 通过对其色散曲线对比分析表明: 当光子晶体光纤孔间距在1 μm附近时, 其色散系数随着孔间距Λ和占空比d/Λ的增大而增加, 但对于孔间距Λ的变化比占空比d/Λ更为敏感, 并且随着孔间距Λ的增加,其对色散系数的影响能力逐渐减小. 设计并制备的光子晶体光纤在1550 nm处的色散系数为-241.5 ps·nm^-1·km^-1, 相对色散斜率为0.0018, 具有较好的色散补偿能力. 关键词： 色散 色散补偿 光子晶体光纤 结构参数     

基于分数导数研究高强度聚焦超声的非线性声场

在高强度聚焦超声(high intensity focused ultrasound, HIFU) 的研究中, 生物组织的衰减和色散性质会对声能量的空间分布产生影响. 本文提出应用分数导数修正非线性Khokhlov-Zabolotskaya-Kuznetsov (KZK)方程, 研究生物组织中非线性HIFU声场. 对三种生物仿体的衰减和声速色散的理论实验研究表明分数导数应用的可行性, 在此基础上通过数值仿真分析研究了衰减及声速随频率的变化对HIFU焦域分布的影响. 研究结果表明, 在计算强非线性聚焦超声时, 由于高次谐波的强色散作用, 引入分数导数来解决生物组织特殊的衰减以及色散问题可进一步提高HIFU治疗的安全性. 关键词： 分数导数 声衰减 色散 高强度聚焦超声     

室温磁制冷主动式磁蓄冷器数值模拟

提出了一个研究工作参数、设计参数对主动式磁蓄冷器(AMR)制冷性能影响的数值模型。三个主要参数包括:质量流量m、频率f、蓄冷器孔隙率ε,被用来表征AMR的制冷能力。数值模拟的结果表明:对一个AMR而言,存在一个最佳孔隙率;在某一确定孔隙率条件下,AMR存在最佳换热流体质量流量和最佳工作频率;与高频相比,AMR在较低频率下有更好的制冷性能,一味提高频率并不一定能提高AMR的制冷量。模拟结果对磁制冷样机的设计、工作参数的选择有很大的指导意义。