Influence of nonlinear dispersion on modulation instability of coherent and partially coherent ultrashort pulses in metamaterials

The combination of dispersive magnetic permeability with nonlinear polarization leads to a series of nonlinear dispersion terms in the propagation equations for ultrashort pulses in metamaterials. Here we present an investigation of modulation instability (MI) of both coherent and partially coherent ultrashort pulses in metamaterials to identify the role of nonlinear dispersion in pulse propagation. The Wigner–Moyal equation for partially coherent ultrashort pulses and the nonlinear dispersion relation for MI in metamaterials are derived. Combining the standard MI theory with the unique properties of the metamaterial, the influence of the controllable first-order nonlinear dispersion, namely self-steepening, and the second-order nonlinear dispersion on both coherent and partially coherent MI, in both negative-index and positive-index regions of the metamaterial for all physically possible cases is analyzed in detail. For the first time to our knowledge, we demonstrate that the role of the second-order nonlinear dispersion in MI is equivalent to that of group-velocity dispersion (GVD) to some extent, and thus due to the role of the second-order nonlinear dispersion, MI may appear in the otherwise impossible cases, such as in the normal GVD regime. PACS 42.25.Kb; 42.65.Sf; 78.20.Ci     

针板型触发电晕稳定开关的特性

 为了验证在空气状态下电晕稳定开关的重复频率特性,对自行研制的盘式触发三电极电晕稳定开关的工作特性进行了实验研究,并分析了实验结果。结果表明,在空气状态下,开关具有良好的触发特性,开关抖动和导通时延最小可以分别控制在4, 36 ns;同时,还可以通过减小触发间隙,进一步减小开关的导通时延和增加开关的稳定性。     

Evolution of cooperation among mobile agents

We study the effects of mobility on the evolution of cooperation among mobile players, which imitate collective motion of biological flocks and interact with neighbors within a prescribed radius R. Adopting the the prisoner’s dilemma game and the snowdrift game as metaphors, we find that cooperation can be maintained and even enhanced for low velocities and small payoff parameters, when compared with the case that all agents do not move. But such enhancement of cooperation is largely determined by the value of R, and for modest values of R, there is an optimal value of velocity to induce the maximum cooperation level. Besides, we find that intermediate values of R or initial population densities are most favorable for cooperation, when the velocity is fixed. Depending on the payoff parameters, the system can reach an absorbing state of cooperation when the snowdrift game is played. Our findings may help understanding the relations between individual mobility and cooperative behavior in social systems.     

Fabrication of flower-shaped Bi2O3 superstructure by a facile template-free process

A novel flower-shaped Bi₂O₃ superstructure has been successfully synthesized by calcination of the precursor, which was prepared via a citric acid assisted hydrothermal process. The precursor and Bi₂O₃ were characterized with respect to morphology, crystal structure and elemental chemical state by field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). It was shown that both the precursor and Bi₂O₃ flower-shaped superstructure were constructed of numerous nanosheets while the nanosheets consisted of a great deal of nanoparticles. Furthermore, key factors for the formation of the superstructures have been proposed; a mechanism for the growth of the superstructure has been presented based on the FESEM investigation of different growth stages.     

相对论重离子反应的热化过程

本文从相对论BUU理论出发研究了1GeV/n能区重离子反应全局(global)和局域(local)平衡性质,计算表明在该能区平均场对反应动力学过程仍有相当的作用;对有限核系统的反应动力学过程的时间演化的研究表明,有限核系统无论全局的还是局域的平衡均未能达到完全平衡,因而对有限核系统重离子反应基于完全热平衡概念的适用性值得怀疑.     

An Economical Magnetocardiogram System Based on High-To SQUIDs

An economical magnetocardiogram （MCG） system is built in our laboratory. It mainly consists of a MCG data acquisition stage equipped with two high-To superconducting quantum interference device （SQUID） magnetometers, a data processing stage with digital filtering and a one-layer μ-metal magnetically shielded room in conjunction with a high-Tc SQUID based active compensation. Experimental results show that a noise level of pico-tesla in MCG profiles, which is necessary for clinical applications, may be achieved with the system. Moreover, stable and convenient operations of the system are demonstrated with simulating MCG measurements.     

Two Stable Heterometal‐MOFs as Highly Efficient and Recyclable Catalysts in the CO2 Coupling Reaction with Aziridines

Two stable heterometal‐organic frameworks, {Na[LnCo(DATP)₂(Ac)(H₂O)](NO₃)?DMA?11 H₂O}_n (Ln=Er( 1 ) and Yb( 2 )), have been prepared with H₂DATP (4′‐(3,5‐dicarboxyphenyl)‐2,2′:6′,2′′′‐terpyridine) as organic building block. These two isostructural compounds featuring two‐dimensional layer architectures possess outstanding thermal stabilities and excellent chemical stabilities in common organic solvents and different acid/base solutions with pH range changing from 1 to 13. Moreover, compounds 1 and 2 serving as heterogeneous catalysts can efficiently catalyse the CO₂ fixation reaction with various aziridines to result in corresponding oxazolidinones at 70 °C. Importantly, a good recyclable performance of 1 for at least 10 cycles is observed based on the experimental results, which are further confirmed by PXRD, TGA and ICP analyses.     

有限混合Gamma分布的拓扑稠密性证明

首先给出了有限混合Erlang分布在正实数轴上所有概率分布中稠密的理论证明,进而给出了混合Gamma分布具有稠密性的结论,说明有限混合Gamma分布具有广泛的适用性,可以用来刻画正实数轴上的任意随机变量.     

Improvement in Dielectric Tunability of Ba0.6Sr0.4TiO4-Mg2TiO4 Composite Ceramics via Heterogeneous Nucleation Processing

Dielectric tunable composite ceramics Ba0.6Sr0.4 TiO4-Mg2 TiO4 （BST-MT） are prepared with a heterogeneous nucleation sol-gel approach. The Mg2 TiO4 powders are synthesized by the conventionM solid-state reaction method. The micro-sized MT powders with dispersant Ciba-4010 are introduced into Ba-Sr-Ti sol to obtain uniform and homogeneous mixture compounds with nano-sized BST particles synthesized via heterogeneous nucleation （HN） in the sol-gel process. Thus, the mierostructural and dielectric properties can be tailored. The dielectric constants of BST-MT composite ceramics can be adjusted in a larg＇e range from 294 to 1790, and the dielectric tunability can be adjusted from 29.4% to 37.0% with different MT contents from 60wt% to 20wt%. Compared to the samples prepared by the conventional solid-state （SS） process, the BST-MT composite ceramics by the heterogeneous nucleation sol-gel process exhibit a more uniform microstructure, and improve dielectric properties.