The Topology Sampling of H2SO4·NH3 with Meta-Dynamics Method

The configurations of molecular clusters have significant impacts on their growth into fine particles in atmosphere. In this paper, we explore the topology space of the structure of H2SO4·NH3 dimer with a novel sampling technique of meta-dynamics (MTD) method and ab initio molecular dynamics simulations. The simulations are carried out at the temperatures of both 50 K and 242 K, which represent the typical high and low latitudes of troposphere. The results show that, compared with only traditional MD simulations, the structure samplings are significantly accelerated with MTD method. Therefore, more isomers of the dimer are discovered within the same simulation time scale. In addition, the results show that MTD is more efficient for circumstances with high temperature.     

基于密钥共享的分层混合认证模型

随着信息时代的迅速发展,云计算数据访问安全已经成为了用户最关心的问题。身份认证技术是确保参与者在开放的网络环境中实现安全通信的一种重要手段,如何利用身份认证技术为云环境安全保驾护航,成为学者研究的热点。文中通过公钥基础设施(Public Key Infrastructure,PKI)颁发CA证书以在不同云服务间建立信任,将多个采用身份密码体制(Identity-Based Encryption,IBE)的云联合起来；采用分层身份加密体系,引入共享密钥技术,通过选取成环结构,提出一种PKI-IBE混合认证模型方案,并对方案的安全性进行分析,从理论上证明了云环境下PKI-IBE(Public Key Infrastructure-Identity-Based Encryption)同层成环模型提供服务的可行性。同时文中设计了一种基于该模型的签密技术,通过公私密钥对实现云内认证以及跨云认证。安全性理论证明与性能分析表明,该方案在计算量稍增加的前提下,保证了足够的安全性,更加满足云环境下的用户分属不同云域的认证以及用户安全访问的需求,有效解决了云环境中数据访问的安全问题。     

Self-assembly of ultralight and compressible inorganic sponges with hierarchical porosity by electrospinning

The construction of three dimensional macroporous architectures holds exciting implications for applications such as catalysis, sensing, tissue engineering and thermal insulation. Here, we report a general self-assembly process for inorganic sponges with hierarchical porosity of intrafibre micro-/meso-/macropores and interfibre macropores. The as-fabricated SiO₂-TiO₂ sponge possesses a high porosity of >99.86%, ultralow bulk density of 2.9 mg cm⁻³ and enhanced compressibility (recovery from 50% compression). The self-assembly mechanism of the SiO₂-TiO₂ sponge has been investigated in detail. The results confirmed that the hydrolysis and polycondensation of mixed inorganic alkoxides could affect the solidification process and the charge transpote during electrospinning, and plays an essential role on the hierarchical porosity and the self-assembly of the sponge macro-structure. The concerted effects of the solidification and electrostatic repulsion between fibres are responsible for the self-assembly process of the electrospun PVP-SiO₂-TiO₂ sponge. When used as a thermal insulation material, the SiO₂-TiO₂ sponge shows good fireproof performances. The current contribution may guide more construction of functional inorganic macroporous architectures for advance applications in future.     

柔性化夹具静动态特性分析及拓扑优化

针对汽车发动机缸盖、变速箱阀体全自动化混合生产线,设计柔性化夹具来满足CNC高精密加工以及快速换产的要求。建立夹具系统三维模型,并利用ANSYS对夹具系统在不同加工工况载荷下进行静态性能分析;从分析结果判断出影响夹具性能的关键结构,并对其进行拓扑优化设计,实现夹具整体减重39.25 kg。然后对改进后夹具模型进行验证分析,发现最大变形量减少为0.0045199 mm,满足设计指标0.005 mm;最后,对现有夹具系统进行模态实验和CAE模态分析,发现夹具系统在Z向受到低频激振力时,容易发生共振,该频段为70 Hz?110 Hz,在加工过程中需要控制刀具加工频率避免发生共振。     

Non-isocyanate polyurethane (NIPU) from tris-2-hydroxy ethyl isocyanurate modified fatty acid for coating applications

Conventional polyurethanes, in spite of their excellent properties and wide applications possess safety and handling issues related to isocyanate compounds while synthesis. The cyclic carbonate-amine reaction resulting into hydroxyurethane is said to be an isocyanate free polyurethane system and novel route of synthesis as well as good alternative to conventional polyurethanes. In the present work, non-isocyanate polyurethane was synthesized by modification of dehydrated castor oil fatty acid (DCOFA) with tris-2-hydroxy-ethyl isocyanurate (THEIC). The synthesis involved three steps viz esterification of DCOFA with THEIC, epoxidation of the ester formed (TEFA) and subsequent cyclocarbonation of THEIC–ester of fatty acid (CTEFA). The products obtained were confirmed by Fourier Transform Infrared Spectroscopy (FTIR) as well as ¹H and ¹³C Nuclear Magnetic Spectroscopy (NMR). The CTEFA was cured with various amines such as dimethyl diphenyl sulphone (DDS), Isophorone Diamine (IPDA) and hexamethylene diamine (HMDA) to obtain NIPU coatings. The cured coatings were studied for chemical, mechanical, thermal and electrochemical properties. Also, the effect of amine curing agents on the performance of NIPU coatings was investigated. Experimental results showed that incorporation of THEIC into the system significantly improved coating properties.     

Decomposition of first-order hybrid Petri nets for hierarchical control of manufacturing systems

Although hybrid Petri net (HPN) is a popular formalism in modelling hybrid production systems, the HPN model of large scale systems gets substantially complicated for analysis and control due to large dimensionality of such systems. To overcome this problem, a typical approach is to decompose the net into subnets and then control the plant through hierarchical or decentralized structures. Although this concept has been widely discussed in the literature for discrete PNs, there is a lack of research for HPNs. In this paper, a new method of decomposition of first-order hybrid Petri nets (FOHPNs) is proposed first and then the hierarchical control of the subnets through a coordinator is introduced. The advantage of using the proposed approach is validated by an existing example. A sugar milling case study is analysed by using a decomposed FOHPN model and the optimization results are compared against the results of the approaches presented in other papers. Simulation results show not only an improvement in production rate, but also show the ability to control the plant online. In addition, by using the hierarchical control structure for an FOHPN model, it is possible to reduce the cost of communication links, improve the reliability of the system, maintain the plant locally, and partially redesign the system.     

Hierarchical multi-reservoir optimization modeling for real-world complexity with application to the Three Gorges system

High dimensionality in real-world multi-reservoir systems greatly hinders the application and popularity of evolutionary algorithms, especially for systems with heterogeneous units. An efficient hierarchical optimization framework is presented for search space reduction, determining the best water distributions, not only between cascade reservoirs, but also among different types of hydropower units. The framework is applied to the Three Gorges Project (TGP) system and the results demonstrate that the difficulties of multi-reservoir optimization caused by high dimensionality can be effectively solved by the proposed hierarchical method. For the day studied, power output could be increased by 6.79 GWh using an optimal decision with the same amount of water actually used; while the same amount of power could be generated with 2.59 × 10⁷ m³ less water compared to the historical policy. The methodology proposed is general in that it can be used for other reservoir systems and other types of heterogeneous unit generators.     

Design and optimization of ceramic membrane structure: From the perspective of flux matching between support and membrane

The support flux was first investigated as a separate influencing factor for its effect on performances of ceramic filtration membranes. Three pre-membranes were prepared by tape-casting and then transfer-coated to supports to form dual-layer ceramic membranes after sintering. Experiments demonstrated that membrane layers with almost the same properties were obtained despite the huge difference in support flux. When the support flux increases from 3.120 to 97.53 m³m^?2h^?1, the flux of these three membrane series have increased by 75%, 186% and 228%, respectively. Experimental rules can provide structural design and evaluation from the perspective of permeability. The limit membrane flux of a certain system was derived according to the resistance distribution law of internal membrane structure and the Darcy's theorem. On this basis, a method for designing support flux was proposed. Furthermore, we present a criterion to quickly and easily evaluate the match between the support and the top layer, which is the ratio of membrane resistance to total resistance. Finally, the filtration resistance of penetration caused by suction of membrane particles into the support was measured for the first time, taking the advantage of the transfer-coating method that inherently free of penetration. Our works are expected to deepen the understanding of the ceramic membrane structure and provided guidance for its rational design and optimization.     

热稳定处理时间对TNM合金糊状区组织的影响

利用真空非自耗电弧炉制备了TNM(Ti-44Al-4Nb-1Mo-0.1B at.%)合金锭,研究其铸态组织形貌,并利用Bridgeman定向凝固装置对TNM合金进行热稳定处理实验,分析热稳定处理时间对合金定向凝固糊状区的影响。实验结果显示,其铸态组织是以(α₂+γ)片层团为主体,网络状B2相、细小的γ相及硼化物分布于片层团间的近片层组织。热稳定处理时,热稳定时间越长、TNM合金固/液界面越平整,界面前沿温度场和溶质场趋向均匀,但从减少坩埚对熔体的污染的角度考虑,热稳定处理时间不宜过长,30~60 min的热稳定时间即可提供平整的定向凝固启动界面。 热稳定处理影响着TNM合金固/液界面附近固液两相中Al元素的分布,进而影响硼化物的分布。