Impulsive control for a predator-prey Gompertz system with stage structure

For pest control in agriculture, we investigate the dynamics of a stage-structured predator-prey Gompertz system with impulsive spraying pesticide and releasing of natural enemies at different fixed moment. Using the stroboscopic map and comparison theorem, we obtain the sufficient conditions for the global attractivity of the mature predator-extinction periodic solution and the permanence of the system. Numerical simulations are inserted to verify the feasibility of the theoretical results, which show that the impulsive control plays a key role on the permanence of the system and also provide tactical basis for pest control.     

The revised generalized Tikhonov regularization for the inverse time-dependent heat source problem

This paper investigates the inverse problem of finding a time-dependent heat source in a parabolic equation where the data is given at a fixed location. A conditional stability result is given, and a revised generalized Tikhonov regularization method with error estimate is also provided. Numerical examples show that the regularization method is effective and stable.     

Preparation of hierarchical polyaniline nanotubes based on self‐assembly and its electrochemical capacitance

This article reports the preparation and self‐assembly of polyaniline (PANI) nanotubes, which were chemically synthesized by using in situ doping polymerization in the presence of ammonium persulfate (APS; (NH₄)S₂O₈) as the oxidant without the use of an external template. The synthesized hierarchically nanotubes with a shape of a single nanotube with a length of 0.6 to 0.8 µm and an average with of 100 nm assembled from nanoparticles. The effects of the [salicylic acid]/[aniline] ratio on the size and capacitance of PANI nanotubes were studied. The specific capacitance behavior of the PANI nanotubes was also investigated by using cyclic voltammogram and galvanostatic charge–discharge tests. A maximum discharge‐specific capacitance of 422.5 F/g could be achieved, suggesting its potential application in electrode material for electrochemical capacitors. Copyright © 2011 John Wiley & Sons, Ltd.     

CdS纳米棒的水热法制备及形成机理研究

采用水热法以Na2S· 9H2O为硫源,Cd3O12S3·8H2O为镉源,PVP为表面活性剂,成功制备了CdS纳米棒.并利用X射线衍射(XRD)、透射电子显微镜(TEM)和相应选区电子衍射(SAED)、高分辨透射电子显微镜(HRTEM)、X射线能量色散分析谱仪(XEDS)和紫外可见(UV-vis)分光光度计等测试手段对样品的晶体结构、形貌、微观结构和光学特性等特征进行了表征分析,实验结果表明本方法所制备的CdS纳米棒为纤锌矿结构,沿[001]方向择优生长,平均直径大约为50 nm,棒宽均匀、分散性好,带隙为2.43 eV.同时也对CdS纳米棒的形成机理进行了初步探讨,提出了CdS纳米棒的生长模型,其形貌从三角形到阶梯形棒晶,最后再到完整的棒状晶体的一个定向团聚的自组装过程.     

双带频率选择表面设计

为了实现频率选择表面(FSS)的双带特性,设计了由矩形栅格和三圆环组合单元FSS。对FSS的谱域求解方法进行了详细的描述。采用谱域法分析了不同角度和极化入射波下FSS的频率响应性能。结果表明,所设计的FSS对于不同入射角度和极化电磁波具有稳定的双带、平顶传输及陡峭下降边缘特性。双带特性大致表现为1.8～5.4GHz的阻带和5.4～20.0GHz的通带。阻带谐振频率稳定在3.1GHz左右,而通带在-4dB的平顶传输带宽达14.3GHz以上。其陡峭下降边缘特性表现为S波段信号强烈反射,而其他波段信号通过,从而实现多波段通讯。该结构FSS可应用于卫星通信、雷达罩及其他相关领域。     

BaTiO_3纳米颗粒的聚丙烯酰胺凝胶法合成及光催化降解甲基红性能

采用聚丙烯酰胺凝胶法合成了BaTiO3纳米颗粒,利用X射线衍射、傅里叶变换红外光谱、透射电镜和紫外-可见漫反射光谱对样品进行了表征.结果表明,以柠檬酸酸为络合剂、pH=2且在700°C焙烧时可制备出单相BaTiO3纳米颗粒,其形状较为规整,近似呈球形,平均粒径约为55nm,光学带隙值为3.25eV.以偶氮染料甲基红为目标降解物,研究了BaTiO3纳米颗粒的光催化性能.结果表明,在紫外光照射下该纳米颗粒表现出较高的催化活性,光催化机理主要为光生空穴的直接氧化.     

A generalization of the Leggett-Williams fixed point theorem and its application

A generalization of the Leggett-Williams fixed point theorem is established. As an application, the existence of multiple nondecreasing positive solutions for a class of third-order m-point boundary value problems is obtained.     

Slow light engineering in polyatomic photonic crystal waveguides based on square lattice

In this paper, the slow light properties of the polyatomic Photonic Crystal (PhC) which has multiple different air holes in each primitive cell are investigated. A slow light waveguide with “U-type” group index-frequency curve, which results in nearly constant group index over large bandwidth, is achieved using this new photonic crystal geometry based on the square lattice. Also, the radius and position of the innermost rows of small air holes have been modified to investigate the feasibility of controlling the dispersion relation by subtle structural modification. Numerical results demonstrate that decreasing the group velocity effectively and meanwhile maintaining a large Normalized Delay-Bandwidth Product (NDBP) can be achieved by only modifying the radius of the innermost rows of small air holes. Shifting the innermost rows of small air holes toward the waveguide core is highly beneficial to enlarge the slow light bandwidth, but it contributes nothing to the promotion of NDBP. Our results provide important theoretical basis for the potential application offered by the polyatomic photonic crystal in future optical networks.     

Hopf bifurcation in a three-species system with delays

A kind of three-species system with Holling II functional response and two delays is introduced. Its local stability and the existence of Hopf bifurcation are demonstrated by analyzing the associated characteristic equation. By using the normal form method and center manifold theorem, explicit formulas to determine the direction of the Hopf bifurcation and the stability of bifurcating periodic solution are also obtained. In addition, the global existence results of periodic solutions bifurcating from Hopf bifurcations are established by using a global Hopf bifurcation result. Numerical simulation results are also given to support our theoretical predictions.     

对密立根油滴实验的测量方法改进

利用对密立根油滴实验的改进解出了实验操作过程中的各种问题，提高学生的实验兴趣和理论联系实际的能力。