Why C1 = 16–17 in the WLF equation is physical-and the fragility of polymers

From the well-recognized equivalence of the Williams-Landel-Ferry (WLF) equation and the Vogel-Tammann-Fulcher (VTF) equation, τ = τ_o exp (B/[T - T_o]), we shall show that the parameter C₁ in the former is just the number of orders of magnitude between the relaxation time at the chosen reference temperature and the pre-exponent of the VTF equation. Thus C₁^g = log(τ_g/τ_o) (a relation which is not found in the present polymer literature), measures the gap between the two characteristic time scales of the polymer liquid, microscopic and α-relaxation, at the glass transition temperature. For systems which obey these two equations over wide temperature ranges, τ_o is consistent with a quasilattice vibration period in accord with theoretical derivations of the VTF equation and also with the microscopic process of mode coupling theory. Thus for such systems, C₁^g is obliged to have the value 16–17 (depending on how T_g is defined), while C₂^g scaled by T_g will reflect the non-Arrhenius character, i.e. fragility, of the system. In fact when C₁^g has the physical value of 16–17, then (1 − C₂^g/T_g), which varies between 0 and unity, conveniently gives the ‘fragility’ of the polymer within the ‘strong/fragile’ classification scheme. This is useful because it permits prediction from the WLF parameters of other properties such as physical ageing behaviour through the now-established correlation of fragility with other canonical characteristics of glassforming behaviour. Where the best fit C₁^g is not 17 ± 2, the corresponding best fit τ_o must be unphysical, and then the range of relaxation times for which the VTF or WLF equations are valid with a single parameter set will be limited, and the predictions of other properties based on that parameter set will be unreliable. © 1997 Elsevier Science Ltd.     

Application of time–temperature superposition principle to polymer transition kinetics

The time–temperature equivalence equation is deduced simply in view of the transition kinetics of a polymer. The independent variables time and temperature are separated in the two sides of the resulting equation. Thus, a physical property of the polymer, which is temperature dependent, can be matched with the theoretical calculated curve from a supposed model of transition kinetics in which only time is involved as the independent variable. By comparing different models, one may judge which model is probably more correct. The procedure of data fitting is described. As an application example, the measured viscosity data at different temperatures for the coil–globule transition of poly(N‐isopropylacrylamide) in aqueous solution is tested to judge its transition mechanism. A transition mechanism involving a two‐stage reversible reaction fits the experimental data in a satisfactory way. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1767–1772, 2006     

The changing role of diesel oil-gasoil-LPG and hydrogen based fuels in human health risk: A numerical investigation in ferry ship operations

The ships and on-road vehicles are two main emission sources in transportation. In the special form of the ships such as ferry ship, the passengers face with both of two sources because the passengers and vehicles could be proceeding simultaneously. Hence, the exposed emission value in g/m³ by passengers has rapidly increased in the ferries. In this study, the authors found that the vehicles produced emission average 1515 g/s. The calculated value of CO2, SO2, NO2, NO forms respectively, 153.6, 1.37, 0.138, 0.12 g/s. The impatient passengers could be exposed to these emissions more than the reference dose limits within a certain time period. Among these forms, we revealed SO2, NO2 and NO have health risk with HQ value within the 1-year period. The expected symptoms could be summarized respiratory paralysis, damage to liver, lung, spleen, and blood, respiratory and CNS involvement, cancer in long-term.     

大型预应力混凝土渡槽结构受力性能试验研究

本文介绍南水北调中线工程河南段初步设计中提出的跨度为40m，双箱矩形断面大型预应力混凝土渡槽结构的1：5仿真模型试验研究情况，对预应力混凝土渡槽结构仿真模型试验中结构自重的模拟与结构承受水荷载作用前初始应力状态的建立、水荷载施加方法等关键技术问题进行了分析讨论。试验结果表明，采用调整混凝土初始预应力的方法模拟预应力混凝土渡槽结构在结构自重作用的受力状态是可行的。采用单面橡胶和钢结构组成的单腔和多腔加载水囊可以准确地模拟渡槽中水荷载的作用，采用全自动数据采集处理系统是保证大型结构模型试验数据采集同步而精确的必要设备条件，为大型预应力混凝土结构模型试验提供重要成功经验。针对渡槽单箱承受水荷载和双箱承受水荷载时主要构件的性能测试结果，提出各构件的设计方法和结构构造措施以及需要进一步改进的结构设计建议。     

漓江客运码头管理信息化建设的必要性探讨

桂林旅游业是桂林支柱型产业,对桂林的发展贡献显著。本文通过对漓江客运码头信息化现状的描述,发现码头信息化建设薄弱,导致指导监督难、秩序混乱和存在安全隐患、经营管理落后、服务水平低等问题。从而说明桂林漓江客运码头信息化建设在加强主管部门监督和指导、维护公共安全和公共秩序、实现码头科学管理和规范经营、提供公众信息服务平台等方面是必要的。最后提出漓江客运码头管理信息化建设的思路。     

分裂WSN中基于消息摆渡的吞吐率分析

在无线传感器网络(WSN)中,由于节点能量与通信距离的限制,节点间的通信会出现间隙性,甚至产生分裂网络。为此,采用消息摆渡的方法构造网络吞吐率的数学规划问题并进行仿真。实验结果表明,节点的缓存空间、感知速率不影响整个网络的吞吐率,网络吞吐率随摆渡节点移动速度的加快而提高。     

Determinants of injuries in passenger vessel accidents

This paper investigates determinants of crew and passenger injuries in passenger vessel accidents. Crew and passenger injury equations are estimated for ferry, ocean cruise, and river cruise vessel accidents, utilizing detailed data of individual vessel accidents that were investigated by the U.S. Coast Guard during the time period 2001–2008. The estimation results provide empirical evidence (for the first time in the literature) that crew injuries are determinants of passenger injuries in passenger vessel accidents.     

Theoretical–experimental evaluation of different biomaterials for parts obtaining by fused deposition modeling

Although microFDM (microFused Deposition Modeling) has been widely used with biomaterials, there is not enough information about their flow models and the appropriate values for operating conditions. The aim of this paper is to provide a criterion to establish feasible ranges of temperature and shear stress to carry out fused deposition of the biomaterials studied at microscale (hundreds of μm). Materials used were (acrylonitrile–butadiene–styrene), PLA (polylactic acid), and PCL (polycaprolactone). Polyvinyl alcohol was also included in this study, although its quick thermal degradation has led to poor dimensional stability parameters and, therefore, it has been considered inappropriate for this application. Viscosity models were obtained in a 300 μm nozzle microFDM device manufactured by electroforming techniques. These models were used in a simulation analysis whose results show a relationship between the convergence of the algorithm and the characteristics of the filament obtained in equivalent experimental testing.Besides, melt fracture and relevance of swelling was assessed by optical microscopy observation. This information allows to define operating conditions (in terms of temperature and shear rate) to obtain homogeneous morphological characteristics of the microextrudate. Furthermore, the procedure stated could be used in tissue engineering to delimit feasible operating conditions to manufacture scaffolds by fused deposition modeling.     

Artists of the Floating World: SANNA,Niedermayr and the Construction of Atmosphere

Hugh Campbell expands upon the mutually collaborative spatial qualities evoked in the photographic works of Walter Niedermayr and the architecture of Kazuyo Sejima and Ryue Nishizawa of Tokyo-based practice SANAA. Describing their relation as forming a ‘thickened presence’, he alludes to a particular atmosphere reliant on an ambiguity of scale, detail and discernible proximity that serves to liberate the architecture and the photographs from mere documentation whereby instead they figure as transparent recordings of spatial intentions. Copyright © 2008 John Wiley & Sons, Ltd.