186 research outputs found
Opgravingen tussen de Castellumstraat, Het Omloopkanaal en de Oude Rijn
No full textNaar aanleiding van de herstructurering van het centrum van Alphen aan den Rijn vond in de jaren 2001 en 2002 archeologisch onderzoek plaats op de plek waar tussen 40-275 na Chr het castellum Albaniana(e) heeft gelegen. Hierbij werd in 45 werkputten (21-65) ruim een halve hectare onderzocht, waarin sporen uit zeker drie bouwperiodes van het fort te voorschijn kwamen, alsmede kadewerken. Er is een groot deel van de verdedigingswerken aangesneden. Van de binnenbebouwing zijn resten van enkele soldatenbarakken, een fabrica (?), een horreum, de via principalis en enkele waterputten aangetroffen
Mitigating salt damage in lime-based mortars with mixed-in crystallization modifiers
No full textThis paper describes some of the most important results of a four year PhD research on the use of crystallization modifiers mixed in lime mortar to mitigate salt crystallization damage. The research focused on two of the most damaging salts, sodium chloride and sodium sulfate, and suitable crystallization modifiers (sodium ferrocyanide and borax). We report the major findings related to the effectiveness of the modifiers when mixed in the mortar, and the results of characterization of the additivated mortars in comparison with reference mortars. Moreover, the durability of the developed mortars to salt decay is discussed, based on the results of an accelerated salt weathering test carried out in laboratory. No major effects of the modifiers on the fresh and hardened mortar properties were observed which might restrain the application of crystallization modifiers in restoration mortars. Additionally, the mortars with mixed-in modifiers showed a considerable improvement of the salt resistance when compared to reference mortars. Considering these results an outlook for future research pathways is given.Heritage & Technolog
Contact velocities of small ellipsoids settling in turbulence
No full textCollisions of small and heavy non-spherical particles settling in turbulence are very important for systems such as ice clouds and proto-planetary disks where the particle spectra evolution is strongly dependent on the collision induced growth rate. Still, the influence of the particle shape on the collision probability is virtually unknown. Building on our recent investigation on the collision rate of monodisperse suspensions of ellipsoidal particles (Siewert et al., J. Fluid Mech. 758, 686-701, 2014), we show theoretically and by direct numerical simulations that the behavior of ellipsoids subject to turbulence and gravity is different from the behavior of spheres. Due to the dependence of the particle settling velocity on the particle orientation, the relative velocity at contact is influenced by turbulence. When ellipsoids differ either by mass or shape, their contact velocity is randomized by the randomized particle orientation. For particles much heavier than the fluid these orientation dependent settling velocity differences are larger than the relative velocities directly induced by the turbulent fluctuations
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