Tate module and bad reduction

Let C/K be a curve over a local field. We study the natural semilinear action of Galois on the minimal regular model of C over a field F where it becomes semistable. This allows us to describe the Galois action on the l-adic Tate module of the Jacobian of C/K in terms of the special fibre of this model over F.Comment: 13 pages, final version, to appear in Proc. AM

Improved Optimal and Approximate Power Graph Compression for Clearer Visualisation of Dense Graphs

Drawings of highly connected (dense) graphs can be very difficult to read. Power Graph Analysis offers an alternate way to draw a graph in which sets of nodes with common neighbours are shown grouped into modules. An edge connected to the module then implies a connection to each member of the module. Thus, the entire graph may be represented with much less clutter and without loss of detail. A recent experimental study has shown that such lossless compression of dense graphs makes it easier to follow paths. However, computing optimal power graphs is difficult. In this paper, we show that computing the optimal power-graph with only one module is NP-hard and therefore likely NP-hard in the general case. We give an ILP model for power graph computation and discuss why ILP and CP techniques are poorly suited to the problem. Instead, we are able to find optimal solutions much more quickly using a custom search method. We also show how to restrict this type of search to allow only limited back-tracking to provide a heuristic that has better speed and better results than previously known heuristics.Comment: Extended technical report accompanying the PacificVis 2013 paper of the same nam

Do Sales Matter? Evidence from UK Food Retailing

This paper assesses the role of sales as a feature of price dynamics using scanner data. The study analyses a unique, high frequency panel of supermarket prices consisting of over 230,000 weekly price observations on around 500 products in 15 categories of food stocked by the UK’s seven largest retail chains. In all, 1,700 weekly time series are available at the barcode-specific level including branded and own-label products. The data allows the frequency, magnitude and duration of sales to be analysed in greater detail than has hitherto been possible with UK data. The main results are: (i) sales are a key feature of aggregate price variation with around 40 per cent of price variation being accounted for by sales once price differences for each UPC level across the major retailers are accounted for; (ii) much of the price variation that is observed in the UK food retailing sector is accounted for by price differences between retailers; (iii) only a small proportion of price variation that is observed in UK food retailing is common across the major retailers suggesting that cost shocks originating at the manufacturing level is not one of the main sources of price variation in the UK; (iv) own-label products also exhibit considerable sales behaviour though this is less important than sales for branded goods; and (v) there is some evidence of coordination in the timing of sales across retailers insofar as the probability of a sale at the UPC level at a given retailer increases if the product is also on sale at another retailer.Sales, price variation, retail, Consumer/Household Economics, Demand and Price Analysis, L16, L66, Q13.,

Buyer power in U.K. food retailing: a 'first-pass' test

Habtu Weldegebriel, University of Warwick Abstract The potential existence of buyer power in U.K. food retailing has attracted the scrutiny of the U.K.'s anti-trust authorities, culminating in the second of two comprehensive regulatory inquiries in recent years. Such inquiries are authoritative but correspondingly time-consuming and costly. Moreover, detection of buyer power has been dogged by the paucity of reliable evidence of its existence. In this paper, we present a simple theoretical model of oligopsony which delivers quasi-reduced form retailer-producer pricing equations with which the null of perfect competition can be tested using readily available market data. Using a cointegrated vector autoregression, we find empirical results that show the null of perfect competition can be rejected in seven of the nine food products investigated. Though not conclusive on the existence of buyer power, the proposed test offers a means via which the behaviour of the retail-producer price spread is consistent with it. At the very least, it can corroborate the concerns of the anti-trust authorities as to whether buyer power is potentially one source of concern

Buyer Market Power in UK Food Retailing

The potential existence of buyer market power in UK food retailing has attracted the scrutiny of the UK's anti-trust authorities, culminating in the decision to launch the second of two comprehensive regulatory inquiries in recent years. Throughout, detection of buyer power has been dogged by the paucity of reliable evidence of its existence. In this paper we present a simple theoretical model of oligopsony which delivers quasireduced form retailer-producer pricing equations in which the presence of market power can be detected using readily available market data. Using a cointegrated vector autoregression, we find empirical results that are consistent with the presence of oligopsony power in all six food products investigated.Buyer power, Cointegrated VARs, UK food industry, Agribusiness, Consumer/Household Economics,

Dynamics of Food Price Inflation Across the EU

Against the backdrop of recent price spikes on world commodity markets, retail food inflation has varied considerably across EU Member States despite the existence of a range of common policies and, for some Member States, a common currency. In this paper, we investigate the extent and potential causes of the differences in the experience of food inflation through the lens of a single well-defined product chain in 11 EU Member States. Using a structural VAR framework, we find that the contribution of world prices to the behaviour of retail bread prices shows significant differences across the EU Member States we cover. Differences in the functioning of the food sector (particularly barriers to competition and vertical control) appear to be correlated with the role played world prices, highlighting the importance of such structural features in commodity price transmission

Hab-Lab : development of a light touch BPE methodology for retrofit

In the drive toward reduced energy consumption and consequent carbon emissions, and also reductions in fuel poverty and discomfort, the need to improve the performance of existing buildings, particularly housing is critical. To meet government targets some policy drivers are being implemented to improve the performance of existing building. In Scotland this has been through the Energy Efficiency Standard for Social Housing (EESSH) which provides funding for retrofit measures. However, very little is known about the consequences of these measures. This project developed ?light-touch? building performance (BPE) approaches to undertake evaluation of retrofit measures examine their effectiveness and the paper identifies these techniques and reports on the findings. Whilst in general improvements led to reduced energy consumption, various unintended consequences were evident. These included issues of thermal bridging and poor detailing, and lack of improved ventilation provision led to issues of poor ventilation and indoor air quality and reinforces the need for wider evaluation of buildings in use

Performance of private sector health care: implications for universal health coverage

Although the private sector is an important health-care provider in many low-income and middle-income countries, its role in progress towards universal health coverage varies. Studies of the performance of the private sector have focused on three main dimensions: quality, equity of access, and efficiency. The characteristics of patients, the structures of both the public and private sectors, and the regulation of the sector influence the types of health services delivered, and outcomes. Combined with characteristics of private providers-including their size, objectives, and technical competence-the interaction of these factors affects how the sector performs in different contexts. Changing the performance of the private sector will require interventions that target the sector as a whole, rather than individual providers alone. In particular, the performance of the private sector seems to be intrinsically linked to the structure and performance of the public sector, which suggests that deriving population benefit from the private health-care sector requires a regulatory response focused on the health-care sector as a whole