Micro-CT screening of old shell collections helps to understand the distribution of viviparity in the highly diversifed clausiliid clade of land snails

Current zoological research may benefit in many ways from the study of old collections of shells. These collections may provide materials for the verification of broad zoogeographical and ecological hypotheses on the reproduction of molluscs, as they include records from many areas where sampling is currently impossible or very difficult due to political circumstances. In the present paper we present data on viviparous and embryo-retention reproductive modes in clausiliid land snails (subfamily Phaedusinae) acquired from specimens collected since the nineteenth century in the Pontic, Hyrcanian, and East and Southeast Asian regions. X-ray imaging (micro-CT) enabled relatively quick screening of more than 1,000 individuals classified within 141 taxa, among which we discovered 205 shells containing embryos or eggs. Gravid individuals were found to belong to 55 species, representing, for some of these species, the first indication of brooding reproductive strategy

Preliminary structural design of a demountable stadium based on the architectural design of Zwarts & Jansma architects

During this master thesis, research is done on the structural feasibility of a demountable football stadium. To avoid derelict stadiums after one-off events such as the World Cup or Olympic Games, a solution is found in the application of a demountable stadium that can be relocated once a year. The goal of the research is to present a preliminary structural design of a demountable and transportable (football) stadium based on the flying shell concept of Zwarts & Jansma Architects. Based on ideal lines of sight and a limited viewing distance to the centre of the field a distinctive stadium results with an undulating upper edge. The applicability of shell action to create an efficient structural system to the stadium is researched with the help of the method of graphic statics. The 2D results of this study are placed in a 3D context to examine the usefulness to the stadium. Based on these results, four configurations are examined with the help of a computer model to check hypotheses and to gain further insight to allow the design of a final model. A final model is chosen on the basis of behaviour under loading, functionality, ease of assembly and appearance. This final model is tested on ultimate limit situations and serviceability limit state situations. Dynamic behaviour happened to be a critical issue that needed further research. Adjustments to the final model are made to improve the dynamic behaviour of the stadium. In addition to structural behaviour, research is done on the assembly, demountability and transportability of the stadium. Transportation limitations cause the stadium to consist of many small elements that are designed to create maximum uniformity. The order of assembly is based on direct stability, together with shell and ring action providing stiffness during assembly. This is achieved by erecting the stadium layer by layer. The structural system is based on the principle of shell action. Within this principle, double curvature is a very important criterion to ensure structural stiffness. Results of the models that are investigated showed a lack of structural stiffness resulting in a low natural frequency of the total structure. This has major consequences regarding the grandstand structure, as the load spectrum of dynamic crowd loads lies within the response frequency of the grandstand. Either natural frequencies should be increased, or severe measures should be taken regarding the increase of damping capacity, monitoring oscillations in the stadium or design for a dynamic amplification, to rectify this. In order to increase the natural frequency of the stadium the stiffness needs to be increased. The most efficient way to do so with regards to shell action is to increase (double) curvature. Tangential curvature is based on ‘C’ values and preferably should not be altered. Radial curvature is almost absent and needs to be increased. In the situation where natural frequency will not be increased, damping capacity should be increased dramatically by means of the application of dampers at connections or integrated into preassembled elements. The response of the stadium should be monitored and measures taken whenever predefined movements are exceeded. Regarding finance, recurring and non-recurring costs are taken into account. The structural system should be proven to be feasible before financial implications are investigated in more detail.Structural and Building EngineeringDesign and ConstructionCivil Engineering and Geoscience