Enumeration of symmetry classes of convex polyominoes on the honeycomb lattice

Hexagonal polyominoes are polyominoes on the honeycomb lattice. We enumerate the symmetry classes of convex hexagonal polyominoes. Here convexity is to be understood as convexity along the three main column directions. We deduce the generating series of free (i.e. up to reflection and rotation) and of asymmetric convex hexagonal polyominoes, according to area and half-perimeter. We give explicit formulas or implicit functional equations for the generating series, which are convenient for computer algebra.Comment: 21 pages, 16 figures, 2 tables. This is the full version of a paper presented at the FPSAC Conference in Vancouver, Canada, June 28 -- July 2, 200

Charge Density Wave and Superconducting Properties in Single Crystals of Lu5Ir4Si10

We measured the electrical resistivity from 2K up to 900K on high quality single crystals of Lu5Ir4Si10. A clear thermal hysteresis was found at the onset of the Charge Density Wave (CDW), evidencing the first order nature of the transition. When tantalum is included in the compound, the CDW is destroyed and the superconducting critical temperature is enhanced. Finally, we present specific heat and magnetic penetration depth in the Meissner state. We show that the superconducting properties are very close to a weak coupling BCS superconductor

The political economy of derived pension rights

Derived pension rights exist in most Social Security systems but with variable generosity. They are mainly targeted towards non-working wives and widows and are viewed as a means to alleviate poverty among older women living alone. The purpose of this paper is to explain how they can emerge from a political economy process when the Social Security is a combination of Bismarckian and Beveridgian pillars. It also shows that derived rights tend to encourage stay-at- home wives thus revealing an unpleasant trade-o§ between female labor participation and poverty alleviation.social security, derived pension rights, majority voting, individualisation of pension rights

Optimal linear taxation under endogenous longevity

This paper studies the optimal linear tax-transfer policy in an economy where agents differ in productivity and in genetic background, and where longevity depends on health spending and genes. It is shown that, if agents internalize imperfectly the impact of genes and health spending on longevity, the utilitarian social optimum can be decentralized with type-specific redistributive lump sum transfers and Pigouvian taxes correcting for agents's myopia (leading to undersaving and underinvestment in health), and for their incapacity to perceive the effect of health spending on the resource constraint of the economy (causing overinvestment in health). The second-best problem is also examined under linear taxation instruments. Our main result is that it may be optimal to tax health spending, in particular under a complementarity of genes and health spending in the production of longevity.longevity, myopia, genetic background, social security, paternalism

Should we Subsidize Longevity?

This paper studies the design of the optimal non linear taxation in an economy where longevity varies across agents, and depends on three factors: longevity genes, health investment and farsightedness. Provided earnings, farsightedness and genes are correlated, governmental intervention can be justified on two grounds: correction for a lack of farsightedness and redistribution across both earnings and genetic dimensions. Whether longevity-enhancing spending should be subsidized or taxed is shown to depend on the combined effects of myopia, self-selection and free-riding on the annuity returns. Our policy conclusions depend also on how productivity and genes are correlated, on the complementarity of genes and efforts in the survival function, and on how the government weights the welfare of heterogeneous agents. All in all, it might be desirable to tax longevity-enhancing spending.optimal taxation, longevity, genetic background, heterogeneity, myopia

Voting on pensions : sex and marriage

Existing political economy models of pensions focus on age and productivity. In this paper we incorporate two additional individual characteristics: sex and marital status. We ignore the role of age, by assuming that people vote at the start of their life, and characterize the preferred rate of taxation that finances a Beveridgean pension scheme when individuals differ in wage, sex and marital status. We allow for two types of couples: one-breadwinner and two-breadwinner couples. Marriage pools both wage and longevity differences between men and women. Hence singles tend to have more extreme preferred tax rates than couples. We show that the majority voting outcome depends on the relative number of one-breadwinner couples and on the size of derived pension rights.social security, differential longevity, majority voting, individualization of pension rights