The matroid secretary problem for minor-closed classes and random matroids

We prove that for every proper minor-closed class $M$ of matroids representable over a prime field, there exists a constant-competitive matroid secretary algorithm for the matroids in $M$. This result relies on the extremely powerful matroid minor structure theory being developed by Geelen, Gerards and Whittle. We also note that for asymptotically almost all matroids, the matroid secretary algorithm that selects a random basis, ignoring weights, is $(2+o(1))$-competitive. In fact, assuming the conjecture that almost all matroids are paving, there is a $(1+o(1))$-competitive algorithm for almost all matroids.Comment: 15 pages, 0 figure

A disciplinary commons for database teaching

This paper discusses the experience of taking part in a disciplinary commons devoted to the teaching of database systems. It will discuss the structure of a disciplinary commons and our experience of the database version

Can Small and Synthetic Benchmarks Drive Modeling Innovation? A Retrospective Study of Question Answering Modeling Approaches

Datasets are not only resources for training accurate, deployable systems, but are also benchmarks for developing new modeling approaches. While large, natural datasets are necessary for training accurate systems, are they necessary for driving modeling innovation? For example, while the popular SQuAD question answering benchmark has driven the development of new modeling approaches, could synthetic or smaller benchmarks have led to similar innovations? This counterfactual question is impossible to answer, but we can study a necessary condition: the ability for a benchmark to recapitulate findings made on SQuAD. We conduct a retrospective study of 20 SQuAD modeling approaches, investigating how well 32 existing and synthesized benchmarks concur with SQuAD -- i.e., do they rank the approaches similarly? We carefully construct small, targeted synthetic benchmarks that do not resemble natural language, yet have high concurrence with SQuAD, demonstrating that naturalness and size are not necessary for reflecting historical modeling improvements on SQuAD. Our results raise the intriguing possibility that small and carefully designed synthetic benchmarks may be useful for driving the development of new modeling approaches.Comment: 40 pages, 13 figures; preprin

Soil physicochemical characteristics and leaf nutrient contents on banana farms of North Queensland, Australia

Context. Banana production in Australia is in three primary sub-regions within tropical North Queensland and the industry faces a variety of challenges including costs of production, disease and pests, and environmental impacts. The range of soil characteristics and banana leaf nutrient status on banana farms has not previously been systematically described. This knowledge gap makes it difficult to adapt research, management recommendations, and regulations to the needs of the three primary growing sub-regions. Aims. In this work, we aimed to identify key soil factors that differentiate growing sub-regions, and provide context for future research and industry regulation. Methods. We characterised soil and banana leaf samples from 28 banana farms on soil types accounting for >85% of Australia’s banana production. Key results and conclusions. Variation in soil properties and leaf nutrient concentrations were driven largely by site-(principal component 1 in both cases) and management-related variables (principal component 2 in both cases). Management-related foliar nutrient concentrations did not differ between regions despite differences in the associated soil variables. The most important site characteristics appeared to be soil parent material and climate. The Mareeba sub-region has basaltic soils, low rainfall and temperature, whereas the other two sub-regions are hotter, wetter and have a variety of soil parent materials. Leaf nitrogen concentrations were mostly below the regulated limit for additional nitrogen fertiliser application. Implications. Our findings can facilitate sub-regionspecific site selection for research, extension, and monitoring and more targeted regulation of banana production-and environment-related issues

Mesoscale Morphological Change, Beach Rotation and Storm Climate Influences along a Macrotidal Embayed Beach

Abstract: Cross-shore profiles and environmental forcing were used to analyse morphological change of a headland bay beach: Tenby, West Wales (51.66 N; −4.71 W) over a mesoscale timeframe (1996–2013). Beach profile variations were attuned with longer term shoreline change identified by previous research showing southern erosion and northern accretion within the subaerial zone and were statistically significant in both sectors although centrally there was little or no significance. Conversely a statistically significant volume loss was shown at all profile locations within the intertidal zone. There were negative phase relationships between volume changes at the beach extremities, indicative of beach rotation and results were statistically significant (p < 0.01) within both subaerial (R2 = 0.59) and intertidal (R2 = 0.70) zones. This was confirmed qualitatively by time-series analysis and further cross correlation analysis showed trend reversal time-lagged associations between sediment exchanges at either end of the beach. Wave height and storm events displayed summer/winter trends which explained longer term one directional rotation at this location. In line with previous regional research, environmental forcing suggests that imposed changes are influenced by variations in southwesterly wind regimes. Winter storms are generated by Atlantic southwesterly winds and cause a south toward north sediment exchange, while southeasterly conditions that cause a trend reversal are generally limited to the summer period when waves are less energetic. Natural and man-made embayed beaches are a common coastal feature and many experience shoreline changes, jeopardising protective and recreational beach functions. In order to facilitate effective and sustainable coastal zone management strategies, an understanding of the morphological variability of these systems is needed. Therefore, this macrotidal research dealing with rotational processes across the entire intertidal has significance for other macrotidal coastlines, especially with predicted climate change and sea level rise scenarios, to inform local, regional and national shoreline risk management strategies. Keywords: mesoscale morphological change; beach rotation; storm climat

Millennium Villages Evaluation: Midterm Summary Report

This report presents the midterm findings from an impact evaluation of the Millennium Villages Project (MVP) in northern Ghana. The MVP has been designed to demonstrate how an integrated approach to community-led development can translate the international Millennium Development Goals (MDGs) into results. The project in northern Ghana is one of several instigated over the past 10 years, and is set to reach nearly half a million people across 10 countries in Africa. Central to the MVP approach is the synergistic value of integrated community-based investments, focused on scientifically proven interventions, delivered simultaneously rather than as one-off investments. The premise is that a critical platform of basic needs must be reached before economic development can really take off. The project in northern Ghana has been running in three districts since May 2012, investing over £11 million on health, education, agriculture and infrastructure interventions in 35 communities, and reaching around 30,000 people