New Insights into the Setting Processes of Glass Ionomer Cements from Analysis of Dielectric Properties

The setting processes in the commercial glass ionomer cement (Fuji IX Fast) and resin modified glass ionomer cement (Fuji II LC) were investigated by the dielectric spectroscopy. The changes in the real and imaginary parts of the dielectric permittivity [ε*(ω)] as well as dielectric loss (tan δ) with time for Fuji IX Fast show several distinct regions which are related to the different stages of the acid–base reaction. Interestingly, the first stage that lasts for approximately 12 min terminates with a sharp decrease in dielectric parameters which is most probably related to the instantaneous (micro)fracturing of the sample due to a rapid build–up of the shrinkage stress. On the other hand, evolution of the dielectric properties during the setting of Fuji II LC indicates fast reaction in the initial stage (within few minutes) followed by the slow gradual change as a result of the competing nature of the acid–base reaction and light‐activated polymerization.     

Hochselektive Absorberschichten für thermische Sonnenkollektoren

High‐selective absorber coatings for solar thermal collectors Highly selective absorber coatings are necessary for the effective operation of state‐of‐the‐art solar thermal collectors. The thin film gradient optical coating with its spectrally selective characteristics achieves high solar absorptance combined with low thermal emittance. Such complex multi‐layer systems are produced in modular vacuum coating processes. Industrial air‐to‐air coating lines allow the continuous coating of metal bands in a pass‐through process and provide absorber coatings which meet highest demands for efficiency, durability and esthetics.     

Interactive image completion with perspective correction

We present an interactive system for fragment-based image completion which exploits information about the approximate 3D structure in a scene in order to estimate and apply perspective corrections when copying a source fragment to a target position. Even though implicit 3D information is used, the interaction is strictly 2D, which makes the user interface very simple and intuitive. We propose different interaction metaphors in our system for providing 3D information interactively. Our search and matching procedure is done in the Fourier domain, and hence it is very fast and it allows us to use large fragments and multiple source images with high resolution while still obtaining interactive response times. Our image completion technique also takes user-specified structure information into account where we generalize the concept of feature curves to arbitrary sets of feature pixels. We demonstrate our technique on a number of difficult completion tasks.     

Thermal and Electrical Properties of Titanium Between 300 and 1900 K

The specific heat capacity and electrical resistivity of titanium were measured by a subsecond pulse-heating method. Specimens were in the form of a 1.6-mm-diameter-wire. Experiments covered the range between 300 and 1900K; thermometry was provided by Pt10%Rh/Pt and W5%Re/W25%Re thermocouples. The maximum uncertainties in the specific heat capacity and electrical resistivity determinations were less than 3 and 1%, respectively. Results are reported and discussed for both the bcc and hcp structures and the transformation between the two phases.     

Sorption of Pb2+, Cd2+, and Sr2+ Ions on Calcium Hydroxyapatite Powder Obtained by the Hydrothermal Method

The sorption of Pb2+, Cd2+, and Sr2+ ions from aqueous solutions by carbonate-substituted calcium hydroxyapatite (HAP) obtained by the hydrothermal decomposition of urea and calcium–ethylenediaminetetraacetic acid chelates was investigated. The shift of the point of zero charge (pHpzc) of HAP toward lower pH values in solutions of Pb2+ and Cd2+ ions, which was more pronounced for Pb2+ ions than for Cd2+ ions, indicates that specific adsorption of these cations on HAP had occurred. There was no shift of the pHpzc in the solution containing Sr2+ ions, suggesting that specific adsorption of this cation on HAP had not occurred. The sorption isotherms suggest that the sequence of the efficiency of sorption by HAP is Pb2+>Cd2+>Sr2+. Ion exchange is the main mechanism of removal of Sr2+ ions from aqueous solution by apatite, whereas during the sorption of Cd2+ ions, this mechanism occurs simultaneously with the process of specific adsorption. The interaction of the apatite with Pb2+ ions includes the previously mentioned mechanisms and dissolution of the apatite, followed by the precipitation of lead hydroxyapatite.     

Probabilistic Modeling of Walking Excitation for Building Floors

Slender floor structures are becoming increasingly prone to excessive vibration due to human-induced walking excitation. To prevent discomfort of floor occupants and/or malfunctioning of sensitive equipment, it is necessary to have a reliable means of estimating floor vibration in the design phase. For accurate estimation of the floor vibration, both reliable excitation and structural models are required. This paper concentrates on the former by evaluating the performance of the existing force models and suggesting their improvement. For this a force model adopted in the United Kingdom by the Concrete Society was applied to four nominally identical floors using their experimentally identified modal properties. After comparison with experimental data the drawbacks of the force model were identified after which an improved model of the walking-induced dynamic force, based on the combination of two existing methodologies used separately for low- and high-frequency floors, is proposed. The improved model accounts for the intersubject variability in the walking force with respect to the pacing frequency, step length, and forcing magnitude. Moreover, it includes all relevant frequency components of the walking force into analysis, removing the need for classification of floors as low or high frequency. The proposed approach should help designers and building owners to make more informed decisions when evaluating vibration serviceability of floor structures.     

Novel insights into electrical transport mechanism in ionic‐polaronic glasses

Transformation of electrical transport from ionic to polaronic in glasses, which are a potential class of new cathode materials, has been investigated in four series containing WO₃/MoO₃ and Li⁺/Na⁺ ions, namely: xWO₃–(30?0.5x)Li₂O–(30?0.5x)ZnO–40P₂O₅, xWO₃–(30?0.5x)Na₂O–(30.5x)ZnO–40P₂O₅, xMoO₃–(30?0.5x)Li₂O–(30?0.5x)ZnO–40P₂O₅, and xMoO₃–(30?0.5x)Na₂O–(30?0.5x)ZnO–40P₂O₅, 0 ≤ x ≤ 60, (mol%). This study reports a detailed analysis of the role of structural modifications and its implications on the origin of electrical transport in these mixed ionic‐polaron glasses. Raman spectra show the clustering of WO₆ units by the formation of W–O–W bonds in glasses with high WO₃ content while the coexistence of MoO₄ and MoO₆ units is evidenced in glasses containing MoO₃ with no clustering of MoO₆ octahedra. Consequently, DC conductivity of tungstate glasses with either Li⁺ or Na⁺ exhibits a transition from ionic to polaronic showing a minimum at about 20‐30 mol% of WO₃ as a result of ion‐polaron interactions followed by a sharp increase for six orders of magnitude as WO₃ content increases. The formation of WO₆ clusters involved in W‐O‐W linkages for tungsten glasses plays a key role in significant increase in DC conductivity. On the other hand, DC conductivity is almost constant for glasses containing MoO₃ suggesting an independent ionic and polaronic transport pathways for glasses containing 10‐50 mol% of MoO₃.     

Transport of potassium ions in niobium phosphate glasses

The influence of Nb₂O₅ on the structure and ionic conductivity of potassium phosphate glasses was investigated in glasses with composition xNb₂O₅–(100-x)[0.45K₂O–0.55P₂O₅], x = 10–47 mol%. The Raman spectra of glasses reveal a transition from predominantly orthophosphate to predominantly niobate glass network with increasing Nb₂O₅ content. In the glass structure, niobium forms NbO₆ octahedra which are interlinked with phosphate units for the glass containing 10 mol% Nb₂O₅, but for higher Nb₂O₅ content they become mutually interconnected via Nb-O-Nb bonds. The transport of potassium ions was found to be strongly dependent on the structural characteristics of the glass network. While the mixed niobate-phosphate glass network hinders the diffusion of potassium ions by providing traps that immobilize them and/or by blocking the conduction pathways, predominantly niobate glass network exhibits a rather facilitating effect which is evidenced in the trend of DC conductivity as well as in the features of the frequency-dependent conductivity and typical hopping lengths of potassium ions.     

Thermal Properties of Tantalum Between 300 and 2300 K

A subsecond pulse heating method was applied to measure the specific heat capacity, electrical resistivity, total hemispherical emissivity, and normal spectral emissivity of 99.9% pure tantalum in the form of 2-mm-diameter wire. W/Re thermocouple thermometry was applied from 300 to 2300 K, with emissivity measurements above 1300 K involving pyrometric measurements. The maximum uncertainties in the specific heat capacity and electrical resistivity were less than 3 and 1 % respectively. The uncertainty of emissivity measurements was estimated as ±5%. The results are compared with literature values.