Cavity approach for modeling and fitting polymer stretching

The mechanical properties of molecules are today captured by single molecule manipulation experiments, so that polymer features are tested at a nanometric scale. Yet devising mathematical models to get further insight beyond the commonly studied force--elongation relation is typically hard. Here we draw from techniques developed in the context of disordered systems to solve models for single and double--stranded DNA stretching in the limit of a long polymeric chain. Since we directly derive the marginals for the molecule local orientation, our approach allows us to readily calculate the experimental elongation as well as other observables at wish. As an example, we evaluate the correlation length as a function of the stretching force. Furthermore, we are able to fit successfully our solution to real experimental data. Although the model is admittedly phenomenological, our findings are very sound. For single--stranded DNA our solution yields the correct (monomer) scale and, yet more importantly, the right persistence length of the molecule. In the double--stranded case, our model reproduces the well-known overstretching transition and correctly captures the ratio between native DNA and overstretched DNA. Also in this case the model yields a persistence length in good agreement with consensus, and it gives interesting insights into the bending stiffness of the native and overstretched molecule, respectively.Comment: 12 pages; 3 figures; 1 tabl

Entanglement in a multiverse with no common space-time

Inter-universal entanglement may even exist in a multiverse in which there is no common space-time among the universes. In particular, the entanglement between the expanding and contracting branches of the universe might have observable consequences in the dynamical and thermodynamical properties of one single branch, making therefore testable the whole multiverse proposal, at least in principle.Comment: 4 pages. Prepared for the proceedings of the Multiverse and Fundamental Cosmology Meeting (Multicosmofun'12

A Log-linear Homotopy Approach to Initialize the Parameterized Expectations Algorithm

In this paper I present a proposal to obtain appropriate initial conditions when solving general equilibrium rational expectations models with the Parameterized Expectations Algorithm. The proposal is based on a log-linear approximation to the model under study, so that it can be though of as a particular variant of the homotopy approach.The main advantages of the proposal are: i. it guarantees the ergodicity of the initial time series used as an input to the Parameterized Expectations algorithm; ii. it performs well as regards speed of convergence when compared to some homotopy alternatives; iii. it is easy to implement. The claimed advantages are successfully illustrated in the framework of the Cooley and Hansen (1989) model with indivisible labor and money demand motivated via a cash-in-advance constraint, as compared to a procedure based on the standard implementation of homotopy principles.Parameterized Expectations Algorithm, initial conditions, log-linear approximations,homotopy, rational expectations

Early-warning tools to forecast general government deficit in the euro area: the role of intra-annual fiscal indicators

In this paper I evaluate the usefulness of a set of fiscal indicators as early-warning-signal tools for annual General Government Net Lending developments for some EMU countries (Belgium, Germany, Spain, France, Italy, The Netherlands, Ireland, Austria, Finland) and an EMU aggregate. The indicators are mainly based on monthly and quarterly public accounts’ figures. I illustrate how the dynamics of the indicators show a remarkable performance when anticipating general government accounts’ movements, both in qualitative and in quantitative terms. JEL Classification: C53, E6, H6European Monetary Union, Fiscal forecasting and monitoring, General Government Deficit, leading indicators