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Messung der empfundenen Geruchsintensität mit Multigas-Sensorsystemen, das Forschungsvorhaben SysPAQ
(2007)
Measuring perceived air quality and intensity by a Sensor System, the European Project SysPAQ
(2008)
We propose a model to describe the sintering kinetics of polydispersed glass particles, having no adjustable parameter. The model is based on three sintering stages: a pure Frenkel' (F) first step, a mixed Frenkel/MackenzieShuttleworth' stage, and a third, pure MackenzieShuttleworth' (MS) step. The model considers sample shrinkage as the sum of the partial shrinkage of several clusters, each consisting of equally sized particles and each showing independent F or MS behavior. The overall set of clusters mimics the specimen's real particle size distribution. We then introduce the concept of neck forming ability, which allows the formation of necks among particles of different sizes, relaxing the clustering condition. Using experimental physical parameters: particle size distribution, viscosity, surface energy, and the theoretical neck forming ability, the model describes well the sintering kinetics of an alumino-borosilicate glass powder having polydispersed, irregular shaped particles in a variety of temperatures. The sintering kinetics of the real powder is slower, but not far from the calculated kinetics of a monodispersed distribution containing only particles of average size. Thus the model provides a tool for estimating the sintering kinetics of real glass powders, for any size distribution and temperature, thus minimizing the number of laboratory experiments.
Zusammenfassung
Durch die Entwicklung verschiedener Longitudinal- und Transversalwellenprüfköpfe, der variierenden Prüfkopfanordnung und -anzahl in Arrays sowie der verwendeten Erregerfrequenzen stehen derzeit mehrere Ultraschall-Verfahren für Untersuchungen an Betonbauteilen im Echobetrieb zur Verfügung. Darüber hinaus können verschiedene Verfahren für die Auswertung der Messergebnisse, u. a. SAFT-Rekonstruktionsberech-nungen (Synthetic Aperture Focusing Technique), genutzt werden.
Um die Leistungsfähigkeit der Verfahren spezifizieren und auch vergleichen zu können, sind geeignete Kenngrößen erforderlich.
Zu diesem Zweck wurden vorerst drei Kenngröße - das Signal/Rausch-Verhältnis s, die Laterale Auflösung D x und die Gleichmäßigkeit der Abbildung g - definiert und auf Untersuchungsergebnisse zu einem bekannten Prüfobjekt angewendet. Dabei handelt es sich um eine Bohrung in einem Betontestkörper aus Normalbeton B 35, die parallel zur Messfläche eingebracht wurde.
In diesem Beitrag werden die Definitionen und die am Beispiel der Bohrung ermittelten Kenngrößen vorgestellt. Es soll gezeigt werden, dass anhand der vorgestellten Definitionen die Kenngrößen für jedes Verfahren prinzipiell ermittelt werden können. Eine Beurteilung der Werte kann derzeit noch nicht erfolgen. Dazu müssen sich Untersuchungen an weiteren bekannten Objekten anschließen, u. a. auch an gezielt konzipierten Testkörpern, an denen die Einflüsse ausgewählter Objekteigenschaften auf die verfahrensabhängigen Kenngrößen untersucht werden sollen.
Ultrasonic investigation is an established non-destructive testing method for detection of defects and material characterisation. In the last years scanning ultrasonic echo methods were developed especially for the application in civil engineering.
The different scanning ultrasonic echo methods are modified with respect to the type of the transducer applied, the number and the arrangement of transducers and the frequency used. Also different algorithms are used to analyse the measured data, for instance SAFT (Synthetic Aperture Focusing Technique) reconstruction. The results are typically presented as B- and C-scans, obtained from raw data or the SAFT reconstructed data.
Since 2001 several German research institutes co-operate within the scope of the research initiative Non-destructive Evaluation of Concrete Structures Using Acoustic and Electromagnetic Echo-Methods (FOR 384) supported by the Deutsche Forschungsgemeinschaft (DFG). One of the tasks is to investigate these ultrasonic echo methods for special applications like the detection of cavities in concrete structures or faults in tendon ducts.
Concrete test specimens with intentional faults have been manufactured and investigated. Parameters were defined to assess the results more objectively. Currently three parameters -signal/noise-ratio, lateral edge resolution and uniformity- are considered. For the first time results of different working groups on the same imaged objects are compared quantitatively. It should help to get more knowledge about the ultrasonic inspection of typical faults in civil engineering structures.
The effect of elastic stress and relaxation on crystal nucleation in lithium disilicate glass
(2004)
In the framework of a general theoretical approach recently developed, the effect of elastic stresses on the rate of nucleation of crystallites of critical sizes in the process of crystallization of lithium disilicate glasses is studied. Hereby both the evolution of elastic stresses due to changes in the specific volume of the crystallizing system (i.e., differences in the densities of the melt and the crystal) and their relaxation connected with viscous flow are taken into consideration. If the classical theory of nucleation is employed for the determination of the nucleation rates (modified by taking into account elastic stresses), elastic stresses may lead, for the system under consideration, to a decrease of the nucleation rate by up to two orders of magnitude. As shown, the theory allows an at least qualitatively correct incorporation of the effect of elastic stresses and stress relaxation into the description of nucleation phenomena in glass-forming melts.
Cultural Heritage objects are in many cases invaluable and irrecoverable, therefore their protection is a prior goal. One threat arises by intentionally defacing such objects with graffiti. One possibility to face the imminent threat is the application of a surface protection in form of anti-graffiti systems (AGS). However, the knowledge about the performance and durability of AGS on substrates used for historical buildings is still fragmented. The goal of the presented study was to investigate the performance of a newly developed agent in comparison to a selection of commercial anti-graffiti agents on different substrates, which were used for historical buildings. Four commercial anti-graffiti agents with different chemical formulations were selected and tested with the new agent on different stone and brick substrates. The results showed clearly that AGS based on dense, water vapour impermeable coatings are not suitable to porous substrates such as sandstone, brick or porous limestone due to their impair of the hygric properties and the visual appearance of a substrate. The new agent could not completely reach the cleaning efficacy of the dense coatings but exhibited a much lower impact on the properties of the substrate and was therefore better compatible to historical surfaces.