Stability at Random Close Packing

The requirement that packings of hard particles, arguably the simplest structural glass, cannot be compressed by rearranging their network of contacts is shown to yield a new constraint on their microscopic structure. This constraint takes the form a bound between the distribution of contact forces P(f) and the pair distribution function g(r): if P(f) \sim f^{\theta} and g(r) \sim (r-{\sigma})^(-{\gamma}), where {\sigma} is the particle diameter, one finds that {\gamma} \geq 1/(2+{\theta}). This bound plays a role similar to those found in some glassy materials with long-range interactions, such as the Coulomb gap in Anderson insulators or the distribution of local fields in mean-field spin glasses. There is ground to believe that this bound is saturated, offering an explanation for the presence of avalanches of rearrangements with power-law statistics observed in packings

Strongly Secure Communications Over the Two-Way Wiretap Channel

We consider the problem of secure communications over the two-way wiretap channel under a strong secrecy criterion. We improve existing results by developing an achievable region based on strategies that exploit both the interference at the eavesdropper's terminal and cooperation between legitimate users. We leverage the notion of channel resolvability for the multiple-access channel to analyze cooperative jamming and we show that the artificial noise created by cooperative jamming induces a source of common randomness that can be used for secret-key agreement. We illustrate the gain provided by this coding technique in the case of the Gaussian two-way wiretap channel, and we show significant improvements for some channel configurations.Comment: 11 pages, 7 figures, submitted to IEEE Transactions on Information Forensics and Security, Special Issue: "Using the Physical Layer for Securing the Next Generation of Communication Systems

Minimum pricing of alcohol and its impact on consumption in the UK

A complete model of food demand is estimated for UK households, focusing on alcohol consumption both at home and outside. Using EFS data for 2005-06, several AIDS models have been estimated at different aggregation levels, thus defining a hierarchical system which allows for computation of cross elasticities between finely disaggregated food groups. At the bottom level of the system, elasticities for 9 groups of alcoholic drinks are computed, 4 of which corresponding to home consumption, 5 corresponding to outside consumption. Estimates from the upper levels of aggregation are used to acknowledge substitution and complementarity effect between these 9 groups and all other food groups consumed. Based on alcohol content of the different drinks studied, their strength and price per unit of alcohol sold is computed; a price increase is then devised, whereby all drinks must be sold at a minimum price of 50p per unit. This rise in alcohol prices, in combination with price elasticities of demand, indicates consumption changes observed according to different socio-economic characteristics (geographical, age, gender, income, socio-economic group). In spite of a slight substitution effect between alcoholic drinks and other food groups, overall consumption would decrease by 15% at the UK level. Only alcohol sold for home consumption would see an increase in prices, and reduction in sales would generally spare pubs and restaurants. While consuming more units of alcohol than other groups, higher income and high managerial groups would be less affected by this pricing policy.Health Economics and Policy,

Current accounts dynamics in OECD and EU acceding countries - an intertemporal approach

The paper extends the standard intertemporal model of the current account to include two important stylised facts: (1) the persistence of current account positions and (2) the relevance of the fiscal balance. Specifically, the paper derives a closed form solution for consumption in the presence of habit persistence and liquidity constraints, which allows us to obtain a dynamic model for the current account where fiscal deficits have an effect. The model is estimated for a panel of 33 countries, including the ten EU acceding countries and structural current account positions are derived. A parsimonious specification including relative income, relative investment and the fiscal balance explains well past current account developments. A key finding of the paper is that, from an intertemporal perspective, current accounts in most acceding countries are currently broadly in line with their structural current account positions. JEL Classification: F32, F41current account, habit persistence, liquidity constraints, panel