A proposal for comparison of types in Pascal and associated semantic models

A new proposal for type comparison in Pascal is advocated. This proposal is devised to integrate naturally with other aspects of the language. The usual typing conventions are reviewed and the improvements provided by the new proposal are illustrated. Several formal models are developed to support the concepts on which the proposal is based and the equivalence of these models is demonstrated. The presentation includes an algorithmic component sufficient to serve as the basis of an implementation.     

An analysis of competing toughening mechanisms in layered and particulate solids

The relative potency of common toughening mechanisms is explored for layered solids and particulate solids, with an emphasis on crack multiplication and plasticity. First, the enhancement in toughness due to a parallel array of cracks in an elastic solid is explored, and the stability of co-operative cracking is quantified. Second, the degree of synergistic toughening is determined for combined crack penetration and crack kinking at the tip of a macroscopic, mode I crack; specifically, the asymptotic problem of self-similar crack advance (penetration mode) versus $90^{\circ }$ symmetric kinking is considered for an isotropic, homogeneous solid with weak interfaces. Each interface is treated as a cohesive zone of finite strength and toughness. Third, the degree of toughening associated with crack multiplication is assessed for a particulate solid comprising isotropic elastic grains of hexagonal shape, bonded by cohesive zones of finite strength and toughness. The study concludes with the prediction of R-curves for a mode I crack in a multi-layer stack of elastic and elastic–plastic solids. A detailed comparison of the potency of the above mechanisms and their practical application are given. In broad terms, crack tip kinking can be highly potent, whereas multiple cracking is difficult to activate under quasi-static conditions. Plastic dissipation can give a significant toughening in multi-layers especially at the nanoscale.     

Removal of inorganic mercury and methylmercury from surface waters following coagulation of dissolved organic matter with metal-based salts

The presence of inorganic mercury (IHg) and methylmercury (MeHg) in surface waters is a health concern worldwide. This study assessed the removal potential use of metal-based coagulants as a means to remove both dissolved IHg and MeHg from natural waters and provides information regarding the importance of Hg associations with the dissolved organic matter (DOM) fraction and metal hydroxides. Previous research indicated coagulants were not effective at removing Hg from solution; however these studies used high concentrations of Hg and did not reflect naturally occurring concentrations of Hg. In this study, water collected from an agricultural drain in the Sacramento-San Joaquin Delta was filtered to isolate the dissolved organic matter (DOM) fraction. The DOM was then treated with a range of coagulant doses to determine the efficacy of removing all forms of Hg from solution. Three industrial-grade coagulants were tested: ferric chloride, ferric sulfate, and polyaluminum chloride. Coagulation removed up to 85% of DOM from solution. In the absence of DOM, all three coagulants released IHg into solution, however in the presence of DOM the coagulants removed up to 97% of IHg and 80% of MeHg. Results suggest that the removal of Hg is mediated by DOM-coagulant interactions. There was a preferential association of IHg with the more aromatic, higher molecular weight fraction of DOM but no such relationship was found for MeHg. This study offers new fundamental insights regarding large-scale removal of Hg at environmentally relevant regarding large-scale removal of Hg at environmentally relevant concentrations.     

Underwater blast response of free-standing sandwich plates with metallic lattice cores

The underwater blast response of free-standing sandwich plates with a square honeycomb core and a corrugated core has been measured. The total momentum imparted to the sandwich plate and the degree of core compaction are measured as a function of (i) core strength, (ii) mass of the front face sheet (that is, the wet face) and (iii) time constant of the blast pulse. Finite element calculations are performed in order to analyse the phases of fluid–structure interaction. The choice of core topology has a strong influence upon the dynamic compressive strength and upon the degree of core compression, but has only a minor effect upon the total momentum imparted to the sandwich. For both topologies, a reduction in the mass of the front (wet) face reduces the imparted momentum, but at the expense of increased core compression. Conversely, an increase in the time constant of the blast pulse results in lower core compression, but the performance advantage over a monolithic plate in terms of imparted momentum is reduced. The sandwich panel results are compared with analytical results for monolithic plates of mass equal to that of (i) the sandwich panel and (ii) the front face alone. (Case (i) represents a rigid core while (ii) represents a core of negligible strength.) For most conditions considered, the sandwich results lie between these limits reflecting the coupled nature of core deformation and fluid–structure interaction.     

Scale effects in the initiation of cracking of a scarf joint

The singular stress field at the interface-corner of a bi-material scarf joint is analysed for a strip of finite width, w, under remote tension and bending. The two substrates are taken as linear elastic and isotopic. The intensity of the singular stress field is calculated using a domain integral method, and is plotted as a function of joint geometry and material mismatch parameters. It is envisaged that the intensity of singularity can serve as a valid fracture criterion provided the zone of nonlinearity is fully embedded within the singular elastic field. It is assumed that fracture initiates when the magnitude of the corner singularity attains a critical value; consequently, the fracture strength of the joint depends upon the size of the structure. In addition, the interfacial stress intensity factor and the associated T-stress are determined for an edge interfacial crack. When the crack is short with respect to the width of the strip, the stress intensity factor is dominated by the presence of the corner singularity; a boundary layer formulation is used to determine the coupling between the crack tip field and the interface-corner field. The solution suggests that an interfacial crack grows unstably with a rapidly increasing energy release rate, but with only a small change in mode mix. This revised version was published online in July 2006 with corrections to the Cover Date.     

Sandwich Panel Design Using Aluminum Alloy Foam

Metal foams may replace polymer foams in applications where multi‐functionality is important. For example it acts as a structural component in a sandwich panel but also as a cooling system or acoustic damper. Associated with sandwich panel geometry and change in loading one observes three failure modes: face sheet yield, core shearing and indentation under the loading roller.     

Hy:Con: A Strategic Tool For Balancing Hydropower Development And Conservation Needs

Hydropower (HP) is an important renewable energy source contributing 65.7% to Austria's national electricity generation. However, HP is also associated with ecosystem degradations jeopardizing the aims of the EU Water Framework Directive (WFD) and Habitats Directive. Based on the EU Renewable Energy Directive (RED), the Austrian Energy Strategy has defined goals to further increase HP production by 3.5 TWh until 2015. Because national strategies for HP development are widely missing, hydropower plants (HPPs) are planned and approved on a local and regional level, often neglecting the overall optimum for energy supply and ecology. Therefore, a decision support tool (Hy:Con) was developed to integrate the energy‐economic characteristics of planned HPPs and conservation needs of ecologically sensible river stretches. Based on 102 planned HPPs in Austria, Hy:Con identified HPPs with high economic attractiveness and low conservation concerns. The results show that owing to the already high HP exploitation in Austria, only a minor number of projects are without conservation conflicts. Upgrading of existing HPPs was associated with least ecological impacts, while HPPs with reservoirs are favoured over run‐of‐river plants. Cumulated ecological effects of numerous small HPPs are significant, whereas their contribution to overall energy production is comparatively small. Hy:Con represents a strategic instrument that can help decision makers to govern the implementation of the RED and WFD in a transparent way to pinpoint the limitations of future HP development and to avoid conflicts and stranded investments. © 2015 The Autors. River Research and Applications Published by John Wiley & Sons Ltd