Cold and Warm Denaturation of Proteins

We introduce a simplified protein model where the water degrees of freedom appear explicitly (although in an extremely simplified fashion). Using this model we are able to recover both the warm and the cold protein denaturation within a single framework, while addressing important issues about the structure of model proteins

Spectral coarse-graining of complex networks

Reducing the complexity of large systems described as complex networks is key to understand them and a crucial issue is to know which properties of the initial system are preserved in the reduced one. Here we use random walks to design a coarse-graining scheme for complex networks. By construction the coarse-graining preserves the slow modes of the walk, while reducing significantly the size and the complexity of the network. In this sense our coarse-graining allows to approximate large networks by smaller ones, keeping most of their relevant spectral properties.Comment: 4 pages, 2 figure

Putting Proteins back into Water

We introduce a simplified protein model where the solvent (water) degrees of freedom appear explicitly (although in an extremely simplified fashion). Using this model we are able to recover the thermodynamic phenomenology of proteins over a wide range of temperatures. In particular we describe both the warm and the {\it cold} protein denaturation within a single framework, while addressing important issues about the structure of model proteins.Comment: 4 Pages, 4 Figures. To appear on PR

Berry Phase and Ground State Symmetry in H x h Dynamical Jahn-Teller Systems

Due to the ubiquitous presence of a Berry phase, in most cases of dynamical Jahn-Teller systems the symmetry of the vibronic ground state is the same as that of the original degenerate electronic state. As a single exception, the linear H x h icosahedral model, relevant to the physics of C60 cations, is determined by an additional free parameter, which can be continuously tuned to eliminate the Berry phase from the low-energy closed paths: accordingly, the ground state changes to a totally-symmetric nondegenerate state.Comment: RevTex, 4 pages, 3 figure

Directed Polymers on a Factorized Disorder Landscape

We study the Directed Polymer model subject to a particular form of disorder, $\eta(x,t)=\eta_X(x) \eta_T(t)$, recently proposed in biological applications. We find that two new universality classes arise, depending on the the lattice geometry. Using an intermediate model linking the two different orientations continuously, we find that there is a phase transition separating two distinct scaling phases. For both phases we get a reasonable understanding of the nature and values of the exponents, corroborated with numerical results.Comment: 4 pages, 4 .eps figure