Un théorème de duplication pour les forêts algébriques

On caractérise les forêts algébriques dont tous les arbres sont de la forme α(t, t). On utilise cette caractérisation pour montrer que la classe des forêts algébriques n'est par fermée par homomorphisme non linéaire, et pour montrer qu'il existe des forêts reconnaissables généralisées, au sens de Maibaum, dont le feuillage n'est pas une forêt algébrique

ARE FRUIT AND VEGETABLE STAMP POLICIES COST-EFFECTIVE?

In many countries, consumption of fruits and vegetables (F&V) is below recommended levels. We quantify the economic and health effects of F&V stamp policy designed for low income consumers. The analysis combined two models: an economic model which predicts how F&V consumption is affected by a change in policy and a health model which evaluates the impact of a change in F&V consumption in terms of death avoided (DA) and life-years saved (LYS). Finally we computed the costs per DA and LYS as the ratio between the taxpayer cost of the policy and the number of DA and LYS. The main findings of the present study are: (1) F&V stamp policy has a positive and significant impact on the consumption of small F&V consumers of the targeted population, (2) at the aggregate level, this policy has a modest impact on consumption and as a result on health gains, (3) for a given budget allocated to the policy, the cost per DA or LYS decreases when the targeting is smaller, at least as long as consumption remains in plausible values, (4) the policy reduces the health inequalities between low and high income populations, (5) when well designed, F&V stamp policy is as cost-effective as price policy (about 42 k€/LYS).Cost-effectiveness analysis, Fruits and Vegetables, Health Impact Assessment, Health Policy, Agricultural and Food Policy, Consumer/Household Economics, Demand and Price Analysis, Food Consumption/Nutrition/Food Safety, Food Security and Poverty, Health Economics and Policy, D61, I18, Q18,

Greater fruit selection following an appearance-based compared with a health-based health promotion poster

Background: This study investigated the impact of an appearance-based compared to a traditional health-based public health message for healthy eating. Methods: 166 British University students (41 male; aged 20.6±1.9 years) were randomized to view either an appearance-based (n=82) or a health-based (n=84) fruit promotion poster. Intentions to consume fruit and immediate fruit selection (laboratory observation) were assessed immediately after poster-viewing and subsequent self-report fruit consumption was assessed 3 days later. Results: Intentions to consume fruit were not predicted by poster type (β=0.03, p=0.74), but were associated with fruit-based liking, past consumption, attitudes, and social norms (smallest β=0.16, p=0.04). Immediate fruit selection was greater following the appearance-based compared to the health-based poster (β=-0.24, p<0.01), and this effect remained when controlling for participant characteristics (β=-0.21, p<0.01). Subsequent fruit consumption was greater following the appearance-based compared to the health-based poster (β=-0.22, p=0.03), but this effect became non-significant on consideration of participant characteristics (β=-0.15, p=0.13), and was instead associated with fruit-based liking and past consumption (smallest β=0.24, p=0.03). Conclusions: These findings demonstrate the clear value of an appearance-based compared to a health-based health promotion poster for increasing fruit selection. A distinction between outcome measures, and the value of a behavioural measure is also demonstrated

Enhanced diffusion due to active swimmers at a solid surface

We consider two systems of active swimmers moving close to a solid surface, one being a living population of wild-type \textit{E. coli} and the other being an assembly of self-propelled Au-Pt rods. In both situations, we have identified two different types of motion at the surface and evaluated the fraction of the population that displayed ballistic trajectories (active swimmers) with respect to those showing random-like behavior. We studied the effect of this complex swimming activity on the diffusivity of passive tracers also present at the surface. We found that the tracer diffusivity is enhanced with respect to standard Brownian motion and increases linearly with the activity of the fluid, defined as the product of the fraction of active swimmers and their mean velocity. This result can be understood in terms of series of elementary encounters between the active swimmers and the tracers.Comment: 4 pages, 2 figures in color, Physical Review Letters (in production