Quadratic and symmetric bilinear forms on modules with unique base over a semiring

Peer reviewed

Assessment of functional forms of crop yield loss models of invasive plant species applied in decision support tools and bioeconomic modelling

AbstractObjectives Decision support tools (DSTs) for invasive species management have had limited success in producing convincing results and meeting users' expectations. The problems could be linked to the functional form of model which represents the dynamic relationship between the invasive species and crop yield loss in the DSTs. The objectives of this study were: a) to compile and review the models tested on field experiments and applied to DSTs; and b) to do an empirical evaluation of some popular models and alternatives. Design and methods This study surveyed the literature and documented strengths and weaknesses of the functional forms of yield loss models. Some widely used models (linear, relative yield and hyperbolic models) and two potentially useful models (the double-scaled and density-scaled models) were evaluated for a wide range of weed densities, maximum potential yield loss and maximum yield loss per weed. Results Popular functional forms include hyperbolic, sigmoid, linear, quadratic and inverse models. Many basic models were modified to account for the effect of important factors (weather, tillage and growth stage of crop at weed emergence) influencing weed–crop interaction and to improve prediction accuracy. This limited their applicability for use in DSTs as they became less generalized in nature and often were applicable to a much narrower range of conditions than would be encountered in the use of DSTs. These factors' effects could be better accounted by using other techniques. Among the model empirically assessed, the linear model is a very simple model which appears to work well at sparse weed densities, but it produces unrealistic behaviour at high densities. The relative-yield model exhibits expected behaviour at high densities and high levels of maximum yield loss per weed but probably underestimates yield loss at low to intermediate densities. The hyperbolic model demonstrated reasonable behaviour at lower weed densities, but produced biologically unreasonable behaviour at low rates of loss per weed and high yield loss at the maximum weed density. The density-scaled model is not sensitive to the yield loss at maximum weed density in terms of the number of weeds that will produce a certain proportion of that maximum yield loss. The double-scaled model appeared to produce more robust estimates of the impact of weeds under a wide range of conditions. Conclusions Previously tested functional forms exhibit problems for use in DSTs for crop yield loss modelling. Of the models evaluated, the double-scaled model exhibits desirable qualitative behaviour under most circumstances.

Report a review of the concepts and definitions of the various forms of relational contracting

Partnering has been defined in many ways. It can be considered as an individual project mechanism or can be considered as a long term strategy. Alliancing is normally assumed to be a long term business strategy linking together client, contractor and supply chain. Relational contracting goes further than this and brings in the whole philosophy of the value chain and the linking of the interdependent parts within the construction project as a key business objective. This document aims to review existing definitions of these three concepts and present and overview of the current state of-the-art in terms of their use and implementation. The document should be useful for all of those project team members looking to sharpen their understanding of the various concepts and will also provide a platform for debating the current state of the definitions and implementations being used in Main Roads and Public Works Departments.

Digital storytelling, podcasts, blogs and vlogs : exploring a range of new media texts and forms in English

Curriculum initiatives in Australia emphasise the use of technologies and new media in classrooms. Some English teachers might fear this deployment of technologies because we are not all ‘digital natives’ like our students. If we embrace new media forms such as podcasts, blogs, vodcasts, and digital stories, a whole new world of possibilities open up for literary response and recreative texts, with new audiences and publication spaces. This article encourages English teachers to embrace these new digital forms and how shows we can go about it.