Dynamics of Symmetric Conserved Mass Aggregation Model on Complex Networks

We investigate the dynamical behaviour of the aggregation process in the symmetric conserved mass aggregation model under three different topological structures. The dispersion a（t, L） = （∑i（mi - ρo ） ^2 / L ）1/2 is defined to describe the dynamical behaviour where Po is the density of particle and mi is the particle number on a site. It is found numerically that for a regular lattice and a scale-free network, σ（t, L） follows a power-law scaling σ（ t, L） ~ t^δ1 and σ（ t, L） ~ t^δ4 from a random initial condition to the stationary states, respectively. However, for a small-world network, there are two power-law scaling regimes, σ（t, L） ~ t^δ2 when t 〈 T and 〈（t, L） ~ t^δ3 when t 〉 T. Moreover, it is found numerically that 62 is near to 61 for small rewiring probability q, and 63 hardly changes with varying q and it is almost the same as 64. We speculate that the aggregation of the connection degree accelerates the mass aggregation in the initial relaxation stage and the existence of the long-distance interactions in the complex networks results in the acceleration of the mass aggregation when t 〉 T for the small-world networks. We also show that the relaxation time r follows a power-law scaling τ ~ L^z and σ（t, L） in the stationary state follows a power-law Gs（L） - L^α for three different structures.     

Formation of Vegetation Patterns and Hysteresis Phenomena in Arid and Semiarid Zones

Considering the spatial effect of the complicated interactions between plant and resource （soil water） and the stochastic character of the complicated ecological processes in an ecosystem, we introduce a lattice gas model to investigate the vegetation pattern formation in the arid and the semiarid ecosystems with Monte Carlo sim- ulations. With consistency of some previous mean-field models, the model reproduces a wide range of patterns observed in the arid and the semiarid regions. The sequences of vegetation states are also investigated with scanning three parameters, i.e., the precipitation and the plant growth rate, and then the parameter ranges are identified where a hysteresis loop appears and two different stable states coexist. The simulation results denote that the complex structures occur only when the precipitation parameter decreases. Moreover, based on the model, it is found that an increase of the competition of the plant for the resource along the slope direction results in the regular stripes parallel to the hill＇s contours. The model provides an interesting mechanism to understand the formation of the other regular vegetation stripe in a limited resource condition.     

Kinetic Phase Transition in A2 ＋ B2 → 2AB Reaction System with Particle Diffusion

A lattice gas model for the A2 ＋ B2→2AB reaction system was studied by Monte Carlo simulation in a two- dimensional triangular lattice surface [Phys. Rev. E 69 （2004）046114]. In the model, a reactive window appears and the system exhibits a continuous phase transition to an ＇A＋vaoancy＇ covered state with infinitely many absorbing states. The critical behaviour was shown to belong to the robust directed percolation （DP） universality class. In this study, we find that as the particle A diffusion is considered, the infinitely many absorbing states for the continuous phase transition change into only two： one is that in which all sites are occupied by particle A and the other is that in which there is only one vacant site and other sites are occupied by particle A. Fhrthermore, a parity conserving character appears in the system when the particle A diffusion is included. It is found that the critical behaviour of the continuous phase transition changes from the DP class into the pair contact process with diffusion model （PCPD） class and the parity conserving character has no influence on the critical behaviour in the model.     

离子束表面改性及其在摩擦学中的应用

本文对离子束表面改性的各种方法和技术水平及其在摩擦学中的应用进行了综述,讨论了为使这种技术更加广泛地应用于实际摩擦学体系还必须研究的一些问题。大量文献资料表明,离子注入是改善材料摩擦学性能的一种有效方法。离子束辅助涂层是新近发展起来的一种离子束表面改性技术,包括离子束增强沉积或离子束辅助沉积、离子束混合和离子束反冲注入。利用它可以制得0.05到几个微米厚的涂层。由于界面的相互扩散混合,离子束辅助涂层能更强地与底材结合,并且常比物理或化学气相沉积的涂层更密实。作者认为,离子束技术今后将在两个相关领域中发展,即直接的离子注入和离子辅助涂层,并且指出离子补助涂层技术将拓宽离子束技术在摩擦学中的应用范围。     

高温热化学非平衡气动热试验与仿真技术研究进展

临近空间新型飞行器向全空域、更高马赫数发展,面临的气动热环境会越发恶劣,高温流场气动热预测技术是该类飞行器发展的关键技术之一.高超声速气流通过激波压缩或黏性阻滞减速,分子动能转化为内能,产生了高温.高温引起体分子振动、电子激发,伴随离解、电离反应等一系列复杂气动物理现象,其流场气动热预测面临诸多挑战.文章对高温热化学非平衡气动热预测技术的发展情况进行了分析探讨.首先,阐述了国内外高温气动热地面试验技术的发展历程,重点介绍分析了气动热风洞试验设备的模拟能力及目前试验测试技术的研究水平;然后,调研和讨论了高温气动热数值模拟研究现状,分别从热化学模型、辐射输运和壁面催化/烧蚀等多个角度探讨了热化学非平衡流场气动热数值模拟规律;最后,对气动热预测技术的发展趋势进行了讨论,提出了高温气动热试验与仿真技术后续应重点解决的问题.     

等离子喷涂Al2O3/TiO2纳米复合涂层的制备、结构及摩擦学性能

采用喷雾干燥法对溶胶-凝胶法合成的系列A l2O3/TiO2纳米复合粉体进行造粒,使用等离子喷涂技术制备系列A l2O3/TiO2纳米复合涂层.对涂层结构和形貌分析表明所制备的A l2O3/TiO2纳米复合涂层形成了具有熔融区和半熔融区的双区形态的纳米复合结构.使用UMT-2MT试验机研究了复合涂层的摩擦磨损性能,结果表明复合涂层的磨损率随TiO2含量的增加表现出先降低而后增大的趋势,TiO2质量百分数为10%的纳米复合涂层的磨损率最低;而涂层的摩擦系数随TiO2含量的增加变化不大.复合涂层的磨损机制为裂纹扩展导致的磨损剥落.     

合成蜡粉改性聚四氟乙烯基粘结涂层摩擦学性能的研究

用合成蜡粉改善聚四氟乙烯基粘结涂层并考察了其摩擦磨损性能以及合成蜡粉添加盈对摩擦磨损试验结果重复性的影响。结果表明：合成蜡粉可明显改善聚四氟乙烯基粘结涂层的减摩耐磨性能;随着合成蜡粉添加量的增加,其摩擦磨损试验数据的重复性显著提高,通过对其磨痕形貌和磨痕表层转移物的分析发现,在摩擦过程中,合成蜡粉可阻止偶件金属元素向聚四氟乙烯基粘结涂层摩擦表面的转移和大尺寸磨屑的产生。     

结构光数字栅线法对物体三维形貌的高精度测量

为了对物体的微观三维形貌进行高精度测量,开发了基于结构光的数字栅线三维纹理测量系统,该系统利用解位相的方法进行物体三维高度信息的计算。首先对相位主值的计算,采用了4步等步长相移法采集16幅等步长的相移图像,分成4组分别计算相位主值,再求其平均值作为最终的相位主值。为了滤除噪声及投影仪、CCD相机畸变等各种影响,对采集的条纹图像采用了自适应维纳滤波和小波多阈值方法进行预处理;其次对于位相展开,提出了基于多频的梯度导向相位展开算法,能够有效避开相位间断点,具有稳定的展开结果。实验结果表明,此系统所使用的方法在条纹图的P₀=22.7 mm-1时,获取的三维信息分辨率为2.75 μm,高度信息精度优于0.5 μm,同时具有测量快速,操作简单,无接触等特点,能够满足高精度的微观三维形貌测量的要求。     

激光共聚焦近红外荧光扫描系统光学设计

为了实现对近红外荧光的高分辨率扫描,设计了工作在近红外光谱区的激光共聚焦光学系统。采用结构简单的凹凸双透镜物镜实现了照明光路和发射光路的设计,并采用Zemax软件进行了光学设计和仿真。实验表明:照明光路的聚焦弥散斑小于1 m,照明针孔处的聚焦光斑小于40 m,满足照明针孔的尺寸要求;发射针孔处的聚焦光斑小于10 m,满足探测针孔尺寸要求;同时照明光路和发射光路的MTF曲线的截止频率都分别满足其衍射极限分辨率的要求,照明光路在全视场空间分辨率420 lp/mm处MTF0.08,发射光路在全视场空间频率400 lp/mm处MTF0.07。     

优化教学模式,打造高效数学课堂

"自学质疑,交流展示"课堂教学模式是主体参与型教学模式的具体实施,是数学教学改革的深入和发展.实施先学后教建构式课堂教学模式的目的就在于充分调动学习主体——学生的积极性,引导他们积极主动、生动活泼地学习,培养他们自主学习、合作探究的能力,培养他们分析问题、解决问题的能力.本文从和谐课堂的构建、自学质疑习惯的培养、交流展示的互动等方面对"自学质疑,交流展示"建构式课堂提出见解和看法.