Primordial molecular clouds

It is now well known that a primordial chemistry, involving light elements produced during the nucleosynthesis period, might develop during the hydrogen post-recombination era. In particular, molecular ions and primordial molecules such as H2, HD and LiH will be produced. We summarize this primordial chemistry after the recombination epoch, and then present a simple gravitational collapse model of a cloud. The potentiality of fragmentation of this collapsing protoclouds through the thermal instability is also discussed. We suggest that this study could also be extended to the CO molecule, because the carbon reservoir molecule CO has already been observed in high redshifts objects.Comment: 12 pages, 1 figures, Invited Talk at 3K Cosmology Conference-Roma October 9

Skill Distributions and the Compatibility between Mobility and Redistribution

We study to what extend in a Tiebout economy, the exogenous distribution of skill across agents affects the compatibility between mobility an redistribution. We propose a two-region economy where: i) each region redistributive policy is elected by majority rule (where both cases: myopic and sophisticated voters are considered), and ii) each region wage is endogenously determined by a separated labor market. We find that the compatibility between mobility and redistribution can be guaranteed when either there is a low-skilled region where the median skilled agent is below the mean skill of the region, or/and when there is a high-skilled region where the median skilled agent is above the mean skill of the region.Tiebout Economy; Redistribution; Sophisticated Voting; Majority rule.

Structured sampling and fast reconstruction of smooth graph signals

This work concerns sampling of smooth signals on arbitrary graphs. We first study a structured sampling strategy for such smooth graph signals that consists of a random selection of few pre-defined groups of nodes. The number of groups to sample to stably embed the set of $k$-bandlimited signals is driven by a quantity called the \emph{group} graph cumulative coherence. For some optimised sampling distributions, we show that sampling $O(k\log(k))$ groups is always sufficient to stably embed the set of $k$-bandlimited signals but that this number can be smaller -- down to $O(\log(k))$ -- depending on the structure of the groups of nodes. Fast methods to approximate these sampling distributions are detailed. Second, we consider $k$-bandlimited signals that are nearly piecewise constant over pre-defined groups of nodes. We show that it is possible to speed up the reconstruction of such signals by reducing drastically the dimension of the vectors to reconstruct. When combined with the proposed structured sampling procedure, we prove that the method provides stable and accurate reconstruction of the original signal. Finally, we present numerical experiments that illustrate our theoretical results and, as an example, show how to combine these methods for interactive object segmentation in an image using superpixels

- LOBBY GROUPS AND THE FINANCIAL SUPPORT OF ELECTION CAMPAIGNS

We study a model of competition between two political parties with policy compromise. There is aspecial interest group with well-defined preferences on political issues. Voters are of two kinds:impressionable and knowledgeable. The impressionable voters are influenced by the electioncampaigns. The objective of the parties is to obtain the maximum votes. Parties compete forfinancial support from a given interest group. Each party proposes a plataform in exchange for anamount of campaign funds, and the interest group decides whether to accept or reject each ofcampaign funds, and the interest group decides whether to accept or reject each of theseproposals. We show that parties competition resembles, to a certain extent, Bertrandcompetition. Furthermore, in equilibrium only one party gets funds from interest group. This resultdiffers from the one obtained in a similar model by Grossman and Helpman (1996a) (1996b), inwhich, in equlibrium, both parties are financed by the interest group. This differnce asisesbecause Grossman and Helpman assume that it is the interest group who makes the proposalsto the political parties.Contract proposal, Lobby groups, Policy compromise