Ultrafast time-resolved imaging of femtosecond laser-induced periodic surface structures on GaAs

We report the formation dynamics of periodic ripples on Ga As induced by femtosecond laser pulses（800 nm, 50 fs） via a collinear time-resolved imaging technique with a temporal resolution of 1 ps and a spatial resolution of 440 nm. The onset of periodic ripples emerges in the initial tens of picoseconds in the timescale of material ejection. The periodic ripples appear after irradiation of at least two pump pulses at surface defects produced by the first pulse and the ripple positions kept stable until the formation processes complete. The formation mechanisms of laser-induced periodic ripples are also discussed.     

Second-order two-scale computations for conductive radiative heat transfer problem in periodic porous materials

In this paper, a kind of second-order two-scale （SOTS） computation is developed for conductive-radiative heat trans- fer problem in periodic porous materials. First of all, by the asymptotic expansion of the temperature field, the cell problem, homogenization problem, and second-order correctors are obtained successively. Then, the corresponding finite element al- gorithms are proposed. Finally, some numerical results are presented and compared with theoretical results. The numerical results of the proposed algorithm conform with those of the FE algorithm well, demonstrating the accuracy of the present method and its potential applications in thermal engineering of porous materials.     

Cellular automata model for traffic flow with safe driving conditions

In this paper, a recently introduced cellular automata （CA） model is used for a statistical analysis of the inner micro-scopic structure of synchronized traffic flow. The analysis focuses on the formation and dissolution of clusters or platoons of vehicles, as the mechanism that causes the presence of this synchronized traffic state with a high flow. This platoon formation is one of the most interesting phenomena observed in traffic flows and plays an important role both in manual and automated highway systems （AHS）. Simulation results, obtained from a single-lane system under periodic boundary conditions indicate that in the density region where the synchronized state is observed, most vehicles travel together in pla- toons with approximately the same speed and small spatial distances. The examination of velocity variations and individual vehicle gaps shows that the flow corresponding to the synchronized state is stable, safe and highly correlated. Moreover, results indicate that the observed platoon formation in real traffic is reproduced in simulations by the relation between vehicle headway and velocity that is embedded in the dynamics definition of the CA model.     

基于严格耦合波理论的周期性极化铌酸锂晶体的电光衍射性质分析

采用严格耦合波理论,数值计算了不同参量下周期性极化铌酸锂晶体的电光衍射性质.研究表明:周期性极化铌酸锂晶体的周期性畴反转结构在电场的作用下相当于折射率衍射光栅,衍射性质和晶体的几何结构、周期、施加电场和入射角密切相关.以布喇格角度入射并满足布喇格衍射条件时,0级衍射光能量随施加电场的增大周期性地转化到-1级的衍射光中,最大转化效率达100%,增大周期性极化铌酸锂晶体的长度可以有效地降低转换电压值;以布喇格角度入射但光传输不满足布喇格衍射条件时,0级衍射光和-1级衍射光不能进行100%的能量转换,同时调制的周期性受到破坏.以布喇格角的倍数角入射时,0级光能量可以转化到相应的其他较高衍射级次,其中奇倍数衍射级的最大转换效率可达100%.研究结果为基于PPLN的集成电光器件设计提供有价值的参考.     

函数概念的“影子化”教学浅探

<正>函数概念是中学数学教学中极其重要的一个组成部分.如何最优化地进行教学,已有不少教育工作者探究过.前苏联教育家巴班斯基说过:"概念、范畴、原则和规律等这些形式的思维永远依靠感性认识,依靠实践活动.""如果其中有视觉,触觉和听觉等各种感觉器官参与,则收效最大."     

周期与季节性因素影响下的短生命周期产品预测优化模型

短生命周期产品因为需求的随机性和产品价值的瞬间变化性,对预测准确性提出了更高的要求.然而许多企业在使用多种预测模型后发现其预测准确率并没有得到显著提升.以短生命周期产品需求特点为背景,在需求预测影响的BASS模型基础上,建立受生命周期和季节性因素影响的需求预测优化模型,最后通过一个产品的实例证实了验证了模型的合理性.     

Research and application of regular phenomenon between periodic signals

The phase change between periodic signals is regular. Research on the regular phenomenon between periodic signals is helpful to improve the precision of some measurements and develop some new measurement methods. So it is necessary to analyze the characteristics of the greatest common factor frequency and the least common multiple period universally existing in periodic signals. The regulation of the quantitative phase shift resolution between periodic signals is presented.The cause of difference in phase characteristics between periodic signals is explained well. In this paper we propose different application prospects based on the regular phenomenon between periodic signals, with focusing on the methods for high precision frequency measurement and transient stability measurement. The experimental results are satisfactory.     

GLOBAL EXISTENCE AND ASYMPTOTIC BEHAVIOR FOR THE 3D COMPRESSIBLE NON–ISENTROPIC EULER EQUATIONS WITH DAMPING

We investigate the global existence and asymptotic behavior of classical solutions for the 3D compressible non-isentropic damped Euler equations on a periodic domain. The global existence and uniqueness of classical solutions are obtained when the initial data is near an equilibrium. Furthermore, the exponential convergence rates of the pressure and velocity are also proved by delicate energy methods.     

HOMOGENIZATION OF THE INCOMPRESSIBLE NAVIER-STOKES FLUID WITH OSCILLATION COEFFICIENT

We study the homogenization of the incompressible Navier-Stokes equations with periodic oscillating coefficient in a bounded non-homogeneous media. To do that, we introduce a generalized compensate compactness result and a suitable class of test function to this problem. By passing the limit, we obtain the homogenized model of this problem.     

TiO2-SnO2纳米晶膜紫外光照下对臭氧气敏性能的研究

以低温水热法制备了TiO2-SnO2复合纳米晶粒,采用提拉法涂敷于带有金电极的氧化铝陶瓷管表面形成敏感薄膜,设计了一种新型薄膜式臭氧传感器。采用X射线衍射仪、热场发射扫描电子显微镜、能量色散X射线谱仪和紫外-可见光谱能谱仪,表征了TiO2-SnO2纳米晶粒的晶体结构和微观形貌。采用紫外-可见吸收光谱法和电化学方法,讨论了TiO2-SnO2纳米晶粒对臭氧敏感机理与光电化学特性。在气体传感器静态测试系统上,采用XEDWS-60A型气敏元件分析仪测试了紫外光下臭氧传感器敏感特性、动态响应、抗干扰和稳定性。结果表明,以Ti与Sn摩尔比为6的TiO2-SnO2纳米晶粒为敏感薄膜的臭氧传感器,在相对湿度为40%和温度为25℃条件下,臭氧浓度为0.1~1.8μg/L时,有、无紫外光照射的臭氧传感器线性度分别为97.5%和78.5%,动态响应分别为2和9 s,恢复时间分别为5.5和15 s。此传感器对CO、NOx、甲醛、丙酮、丁醇和甲醇等气体具有良好的抗干扰性能。在汽车上连续使用12个月后,响应衰减了4.7%,响应正常时间为8.5个月。