H2在Mo x S y 团簇上吸附解离的尺寸效应研究

浆态床加氢工艺可以处理不同来源的劣质重油、渣油,氢气的活化是重油加氢处理过程中发生的主要反应之一。钼基催化剂的分散性是影响重油加氢活性的关键因素。构建了Mo₇S₁₅、Mo₁₂S₂₆、Mo₁₈S₃₉、Mo₂₅S₅₄和Mo₃₃S₇₁团簇,利用密度泛函理论研究了团簇自身的稳定性、活性以及H₂在不同尺寸团簇上的吸附与解离过程。结果发现,在目前所建立的团簇中,其尺寸越小,结合能越低,最高占据分子轨道-最低未占分子轨道(HOMO-LUMO)能隙值越小,团簇稳定性越弱,活性越强。H₂在簇上的稳定吸附位点为边缘位点。随团簇尺寸增大,吸附能分别为-64.25、-34.60、-34.14、-7.20、-6.82 kJ/mol,吸附能绝对值减小,氢气分子与团簇的相互作用减弱,并且解离能逐渐增大,分别为13.76、33.14、53.64、60.75、64.47 kJ/mol。目前的结果表明,团簇尺寸越小,氢气的吸附解离越容易,显示出更高的活性。     

机械故障特征提取的拓扑集分形稀疏字典

多尺度字典是实现机械动态信号中频域弱相干成分解耦的重要方法,但目前还欠缺围绕固定频率进行分辨率持续细化的系统性理论。基于近似解析小波变换构建了全新的拓扑集分形多分辨理论。提出了中心嵌套子空间簇,它随分析尺度深化实现了机械故障特征多目标同时追踪细化,在频域上表现为围绕一系列固定中心频率进行严格的二进细化。在数学上严格证明了:①任意中心嵌套子空间簇都是动态信号频域的拓扑空间;②各中心嵌套子空间簇按分析尺度具有严格自相似的分形特性。另外研究还揭示了二进制多分辨理论与拓扑集分形的深刻同构关联,即任意二进小波包唯一从属于某个中心嵌套子空间簇。其次,在扩展中心嵌套子空间诱导下,经典小波包变换可以化归成拓扑集分形的真子集。将拓扑集分形与旋转机械部件损伤动态模型结合提出了一种新的机械故障特征提取方法。该方法通过周期性成分稀疏测度优化和中心嵌套子空间搜索对冲击性机械故障特征的周期、瞬时动力学参数进行优化提取,从而提取物理意义更显著的单分量信息。将该方法应用于滚动轴承的故障诊断中,在含强噪声的振动信号中准确提取了表征轴承外圈剥落的多个单一模式分量。通过对比验证了所提出方法的噪声抑制能力显著优于以谱峭度和群组稀疏优化为代表的对主流机械故障特征提取技术。     

Size dependence of energy gaps in small carbon clusters: the origin of broadband luminescence

The visible broadband luminescence from carbon-related films has recently been attributed to the band-tail states caused by the variations in the energy gap of individual sp² carbon clusters due to their difference in size and/or shape. In this paper, these band-tail states are classified into two parts: localized and confined. The localized states result from the structural deviation from graphite-like configuration, and the associated luminescence may be described by using the conventional theory for amorphous materials. The confined states are generated due to the existence of stable graphite-like local structures with various sizes and are the main factor for giving efficient, room-temperature luminescence. Our calculations of a series of small hexagonal carbon clusters with first-principle and semi-empirical methods demonstrate that the energy-gap distribution, due to the difference in size, is considerably broad, which may explain the broadband feature of luminescence. Calculations for some tetrahedral clusters were also made for comparison.     

Counterion Interaction and Association in Metal-Oxide Cluster Macroanionic Solutions and the Consequent Self-Assembly

The interaction between large metal-oxide polyanions and their counterions is unique. Owing to their size disparity, there is a moderate ion-pairing effect and loose distribution of counterions around macroions, which leads to the unique solution behavior and the self-assembly of the macroions in polar solvents, and the counterion exchange capability around macroions. Furthermore, the macroion–counterion interaction also affects the catalytic behavior of the polyoxometalate (POM) clusters. Replacement of functionalized cations helps to modify the POM anions through static charge attraction. At the same time, the strong POM–counterion interaction can also lead to counterion-dependent synthesis. Recent developments on theoretical simulations help to understand this interaction at the molecular scale. This review summarizes the chronological progress of the exploration of macroion–counterion interaction (both theoretically and experimentally) and its impact on related research fields.     

公路施工现场单个堆料场修正重心法选址研究

公路工程项目施工现场材料堆料场的合理选址可以优化施工现场材料运输路径,有效减少材料二次搬运,改善现场交通环境,有助于实现施工现场的成本控制和文明施工。但现阶段堆料场选址都是凭借经验确定的,缺少科学的方法对其进行规范,为改善这种现象,分析比较了配送中心与公路工程项目施工现场堆料场的相似性,将单个配送中心选址方法中较经典的重心法进行修正后用于确定公路施工现场单个堆料场的选址,并用算例验证了其可行性。     

基于GVT的公园游憩偏好分析及管理 对策——以上海世纪公园为例

城市综合公园是城市人居生态的重要组成部分。处理好城市公园与居民的关系,在满足公园服务功能的同时保障公园自身的良性环境,是当今城市公园建设的重要课题。以上海世纪公园为研究对象,基于游客轨迹数据和补充问卷调研分析了游客游憩偏好。结果显示,受景观资源不均衡分布的影响,游览路径表现出主路聚集、区域分散的现象;停留空间与游客需求相关,其中老年、中青年和家庭3类典型游客的主要停留节点分别是休憩服务设施、公园植物景点和游乐活动场所。针对环湖区域游客集中的问题,从亲水因素的角度开展分析,发现景观和设施资源分配的不均导致游客对空间亲水性的依赖差异。结合游客群体的游憩偏好特征,重点针对老年和中青年游客提出了公园管理和场地更新建议,助力解决临水区域游客压力过大的问题。     

INFLUENCE OF ALLOYING ELEMENTS ON HYDROGEN DIFFUSION USING SCM-DV-Xα

The influence of alloy composition (Ti,Mn,TiN) on hydrogen diffusion in Fe was studied in detail using SCM-DV-Xα method.The voltage barriers were obtained via calculation on Fe clusters containing the alloy elements such as Ti,Mn as well as the chemical compound TiN respectively.The results showed that Ti element produced deep trap in Fe,decreasing the diffusion coefficient of hydrogen elements，Mn element did not produce deep trap in Fe,decreasing the diffusion coefficient slightly and TiN in Fe produced very deep “trap” decreasing the diffusion coefficient obviously.The calculation results were in agreement with experiment results.     

螺旋齿轮塑件注塑模设计

分析了斜齿轮塑件的工艺特性,给出了实用的注塑模结构,介绍了斜齿轮注塑模各系统的结构设计,论述了模具的工作原理。该模具利用定模推出机构和推管旋转脱模机构解决了螺旋齿轮脱模难的问题。模具结构紧凑,推出可靠,安装维修操作方便,成型塑件质量好,生产效率高。     

浙江余姚模具业发展现状及对策

分析了国内模具业发展状况,同时指出我国模具工业与发达国家相比存在较大的差距,在企业组织结构、产品结构、技术结构、人才、模具园区功能等方面都存在问题.介绍了浙江余姚模具业发展的现状及优势,最后提出了提升余姚模具业竞争力的对策.     

汽车塑料配件注塑模具设计

通过分析两制件的使用要求和结构特点,介绍了一模成型两个不同制件的模具结构特点及模具的动作原理,研究和分析了模具结构采用斜导柱侧抽芯和斜顶相结合,进行内、外侧抽芯成型方案的合理性,给出了模具设计的详细计算过程,实现了一模成型两个不同制件的设想,得出了此模具既方便加工又节约了材料的结论.