A laboratory-numerical approach for modelling scale effects in dry granular slides

Granular slides are omnipresent in both natural and industrial contexts. Scale effects are changes in physical behaviour of a phenomenon at different geometric scales, such as between a laboratory experiment and a corresponding larger event observed in nature. These scale effects can be significant and can render models of small size inaccurate by underpredicting key characteristics such as ow velocity or runout distance. Although scale effects are highly relevant to granular slides due to the multiplicity of length and time scales in the flow, they are currently not well understood. A laboratory setup under Froude similarity has been developed, allowing dry granular slides to be investigated at a variety of scales, with a channel width configurable between 0.25-1.00 m. Maximum estimated grain Reynolds numbers, which quantify whether the drag force between a particle and the surrounding air act in a turbulent or viscous manner, are found in the range 102-103. A discrete element method (DEM) simulation has also been developed, validated against an axisymmetric column collapse and a granular slide experiment of Hutter and Koch (1995), before being used to model the present laboratory experiments and to examine a granular slide of significantly larger scale. This article discusses the details of this laboratory-numerical approach, with the main aim of examining scale effects related to the grain Reynolds number. Increasing dust formation with increasing scale may also exert influence on laboratory experiments. Overall, significant scale effects have been identified for characteristics such as ow velocity and runout distance in the physical experiments. While the numerical modelling shows good general agreement at the medium scale, it does not capture differences in behaviour seen at the smaller scale, highlighting the importance of physical models in capturing these scale effects

The Oxford Dodo. Seeing more than ever before: x-ray micro-CT scanning, specimen acquisition and provenance

The Oxford Dodo (Raphus cucullatus) has been in the collections of the University of Oxford since 1683, first in the Ashmolean Museum and latterly in Oxford University Museum of Natural History. Prior to this the specimen was part of the collections of the Tradescants, father and son, and likely acquired between 1634 and 1656, in the Musæum Tradescantianum in what is now Vauxhall, south London. It has been thought probable that this specimen was once the live bird recorded in London by Sir Hamon L’Estrange in around 1638, but X-ray CT scanning of the skull for anatomical investigation has cast doubt on the provenance of the Oxford Dodo. The 3D visualisation revealed 115 metal particles embedded within the bone of the skull, concentrated in the left side of the skull. All but 5 of the particles are less than 1 mm in diameter and their location leads to the conclusion that they represent lead shot consistent with the bird being shot from the rear right of the head, perhaps with a ventral component. This forensic discovery leaves the provenance of the Oxford specimen uncertain but illustrates the value of non-invasive visualisation techniques in determining the potentially complex histories of unique museum objects

X-ray computed tomography (XCT) and chemical analysis (EDX and XRF) used in conjunction for cultural conservation: the case of the earliest scientifically described dinosaur Megalosaurus bucklandii

This paper demonstrates the combined use of X-ray computed tomography (XCT), energy dispersive X-ray spectroscopy (EDX) and X-ray fluorescence (XRF) to evaluate the conservational history of the dentary (lower jaw) of Megalosaurus bucklandii Mantell, 1827, the first scientifically described dinosaur. Previous analysis using XCT revealed that the specimen had undergone at least two phases of repair using two different kinds of plaster, although their composition remained undetermined. Additional chemical analysis using EDX and XRF has allowed the determination of the composition of these unidentified plasters, revealing that they are of similar composition, composed dominantly of ‘plaster of Paris’ mixed with quartz sand and calcite, potentially from the matrix material of the Stonesfield Slate, with the trace presence of chlorine. One of the plasters unusually contains the pigment minium (naturally occurring lead tetroxide; Pb22+Pb4+O4) whilst the other seems to have an additional coating of barium hydroxide (Ba(OH)2), indicating that these likely represent two separate stages of repair. The potential of this combined approach for evaluating problematic museum objects for conservation is further discussed as is its usage in cultural heritage today

Evaluation of touchable 3D-printed replicas in museums

The multisensory aspect of the museum, while neglected for many years, is undergoing a resurgence as museum workers have begun to push towards re‐establishing the senses as a major component of museum pedagogy. However, for many museums a major roadblock lies in the need to conserve rare objects, a need that prevents visitors from being able to interact with many objects in a meaningful way. This issue can be potentially overcome by the rapidly evolving field of 3D printing, which allows museum visitors to handle authentic replicas without damaging the originals. However, little is known about how museum visitors consider this approach, how they understand it and whether these surrogates are welcome within museums. A front‐end evaluation of this approach is presented, finding that visitors were enthusiastic about interacting with touchable 3D printed replicas, highlighting potential educational benefits among other considerations. Suggestions about the presentation of touchable 3D printed replicas are also discussed

Museum visitor preference for the physical properties of 3D printed replicas

Within museology, the past few decades have seen a resurgence in focus on the experience of the museum visitor and what museum professionals can do to provide more meaningful, memorable visits. One method of achieving this is through multisensory experiences, encouraging museum visitors to use a range of senses to explore an exhibition, a process known to facilitate the generation of memorable experiences. However, as many museum objects are fragile and potentially irreplaceable, surrogates must be created in order to encourage such interaction within exhibitions. Use of 3D printed replicas is one approach, creating risk-free accurate copies of rare objects for visitors to handle. Despite the popularity of this technique, little user experience research has been carried out investigating the perspective of visitors and as a result, little guidance on best practices exist at this stage. Here, we present an investigation into visitor preference of the physical properties of 3D printed replicas, using semantic differentials, exploratory factor analysis and other statistical approaches. The study finds that the most important aspect of 3D prints for museums visitors was that of verisimilitude, visitors dominantly preferring prints that best represented the original specimen, with factors including the robustness of a 3D printed replica and its quality being important to museum visitors, although the importance of these to visitor preference varied. Also discussed are a number of further questions of key interest to heritage workers, including the perspective of the varied nature of museums audience, blind and partially-sighted visitors and their impact on learning experiences

Modelling the penumbra in computed tomography

Background In computed tomography (CT), the spot geometry is one of the main sources of error in CT images. Since X-rays do not arise from a point source, artefacts are produced. In particular there is a penumbra effect, leading to poorly defined edges within a reconstructed volume. Penumbra models can be simulated given a fixed spot geometry and the known experimental setup. Objective This paper proposes to use a penumbra model, derived from Beer’s law, both to confirm spot geometry from penumbra data, and to quantify blurring in the image. Methods Two models for the spot geometry are considered; one consists of a single Gaussian spot, the other is a mixture model consisting of a Gaussian spot together with a larger uniform spot. Results The model consisting of a single Gaussian spot has a poor fit at the boundary. The mixture model (which adds a larger uniform spot) exhibits a much improved fit. The parameters corresponding to the uniform spot are similar across all powers, and further experiments suggest that the uniform spot produces only soft X-rays of relatively low-energy. Conclusions Thus, the precision of radiographs can be estimated from the penumbra effect in the image. The use of a thin copper filter reduces the size of the effective penumbra.</p