水冷型和风冷型日晒色牢度试验机

日晒色牢度试验机自诞生以来，经历了转鼓式风冷、转鼓式水冷和平板式风冷三个时期。该文重点分析了风冷和水冷机型的优缺点，并结合日晒色牢度测试的常用标准和实际应用情况，就风冷和水冷机型对检测结果的影响和不同机型之间检测结果的可比性问题，进行了讨论。     

Modification of Different Zirconium Propoxide Precursors by Diethanolamine. Is There a Shelf Stability Issue for Sol-Gel Applications?

Modification of different zirconium propoxide precursors with H₂dea was investigated by characterization of the isolated modified species. Upon modification of zirconium n-propoxide and [Zr(OⁿPr)(OⁱPr)₃(ⁱPrOH)]₂ with ½ a mol equivalent of H₂dea the complexes [Zr₂(OⁿPr)₆(OCH₂CH₂)₂NH]₂ (1) and [Zr₂(OⁿPr)₂(OⁱPr)₄(OCH₂CH₂)₂NH]₂ (2) were obtained. However, ¹H-NMR studies of these tetranuclear compounds showed that these are not time-stable either in solution or solid form. The effect of this time instability on material properties is demonstrated by light scattering and TEM experiments. Modification of zirconium isopropoxide with either ½ or 1 equivalent mol of H₂dea results in formation of the trinuclear complex, Zr{η³μ₂-NH(C₂H₄O)₂}₃[Zr(OⁱPr)₃]₂(iPrOH)₂ (3) countering a unique nona-coordinated central zirconium atom. This complex 3 is one of the first modified zirconium propoxide precursors shown to be stable in solution for long periods of time. The particle size and morphology of the products of sol-gel synthesis are strongly dependent on the time factor and eventual heat treatment of the precursor solution. Reproducible sol-gel synthesis requires the use of solution stable precursors.     

MCM-41 type materials with low Si/Al ratios

The synthesis of MCM-41 type materials with high amounts of tetrahedral aluminum is reported. Transmission electron microscopy with EDX elemental analysis shows that when using a tetraalkylammonium base in the synthesis of MCM-41 materials Si/Al ratios as low as 12 are possible. In all cases the MCM-41 materials contain an aluminum-rich dense phase in which the aluminum is also tetrahedrally coordinated. This dense phase consumes most of the aluminum of the synthesis mixture.     

Axisymmetric non-Newtonian drops treated with a boundary integral method

A boundary integral method for the simulation of the time-dependent deformation of axisymmetric Newtonian or non-Newtonian drops suspended in a Newtonian fluid subjected to an axisymmetric flow field is developed. The boundary integral formulation for Stokes flow is used and the non-Newtonian stress is treated as a source term which yields an extra integral over the domain of the drop. By transforming the integral representation for the velocity to cylindrical coordinates we can reduce the dimension of the computational problem. The integral equation for the velocity remains of the same form as in Cartesian coordinates, and the Green's functions are transformed explicitly to cylindrical coordinates. Besides a numerical validation of the method we present simulation results for a Newtonian drop and a drop consisting of an Oldroyd-B fluid. The results for the Newtonian drop are consistent with results from the literature. The deformation process of the non-Newtonian drop for small capillary numbers appears to be governed by two relaxation times.     

Non-unique solutions of the Navier-Stokes equations for the Karman swirling flow

Summary In this paper it is shown numerically that axially-symmetric solutions of the Navier-Stokes equations, which describe the rotating flow above a disk which is itself rotating, are non-unique. The numerical techniques designed to calculate such solutions with a high power of resolution are given. Especially the behaviour in and around the first branching point is considered. It is found that fors=–0.16054 two branches coincide. The second branch has been almost completely calculated. It ranges back to positive values ofs.     

Linear-Defect-Induced Thermal Instability in YBCO Thin Films in Microwave Fields

An induced heat instability proposed to explain the difference between microwave properties of YBCO single crystals and thin films at temperatures just below T _c. Extended strain fields near out-of-plane edge dislocations are initial discontinuities for the instability development. We have shown theoretically and have confirmed experimentally that a single dislocation can not have a strong effect on the microwave surface resistance R _s. Dislocation arrays, which were observed experimentally, can induce the thermal instability if edge dislocations in the arrays are spaced closer than the heat relaxation length. Ordered dislocation structures provide much higher local temperature perturbation than randomly distributed dislocations.     

Superprotonic KH(PO3H)–SiO2 composite electrolyte for intermediate temperature fuel cells

Novel thin film composite electrolyte membranes, prepared by dispersion of nano-sized SiO₂ particles in the solid acid compound KH(PO₃H), can be operated under both oxidizing and reducing conditions. Long-term stable proton conductivity is observed at 140 °C, i.e., slightly above the superprotonic phase transition temperature of KH(PO₃H), under conditions of relatively low humidification (pH₂O ≈ 0.02 atm).     

Deductive Model Checking

We present an extension of classical tableau-based model checking procedures to the case of infinite-state systems, using deductive methods in an incremental construction of the behavior graph. Logical formulas are used to represent infinite sets of states in an abstraction of this graph, which is repeatedly refined in the search for a counterexample computation, ruling out large portions of the graph before they are expanded to the state-level. This can lead to large savings, even in the case of finite-state systems. Only local conditions need to be checked at each step, and previously proven properties can be used to further constrain the search. Although the resulting method is not always automatic, it provides a flexible, general and complete framework that can integrate a diverse number of other verification tools.     

Towards Quantitative Structure Determination Through Electron Holographic Methods

The problem of quantitative interpretation of high-resolution electron microscopy is studied in the framework of parameter estimation. Ideally, quantitative interpretation means that unknown structural parameters of an object such as atom types and coordinates are determined from fitting with the experimental dataset. However, in the imaging process, the influence of these parameters is completely scrambled over a large area of the image. As a consequence, the fitting becomes a search process in the higher dimensional space of all coupled parameters. The real importance of holographic methods such as off-axis holography and focus variation is that they restore (deblur) to some extent the imaging process so as to unscramble the influence of the different model parameters. In this way the dimension of the search space becomes manageable. In this framework the concept of resolution in the sense of Rayleigh is not valid anymore, but it has to be replaced by the notice of parameter precision. In case two atoms are very close, the parameter space may become degenerate so that the atoms cannot be discriminated. The probability of this degeneracy is a function of the distance between the atoms and the dose of the imaging particles.