12,437 research outputs found
Fluctuations induce transitions in frustrated sparse networks
We analyze, by means of statistical mechanics, a sparse network with random
competitive interactions among dichotomic variables pasted on the nodes, namely
a Viana-Bray model. The model is described by an infinite series of order
parameters (the multi-overlaps) and has two tunable degrees of freedom: the
noise level and the connectivity (the averaged number of links). We show that
there are no multiple transition lines, one for every order parameter, as a
naive approach would suggest, but just one corresponding to ergodicity
breaking. We explain this scenario within a novel and simple mathematical
technique via a driving mechanism such that, as the first order parameter (the
two replica overlap) becomes different from zero due to a real second order
phase transition (with properly associated diverging rescaled fluctuations), it
enforces all the other multi-overlaps toward positive values thanks to the
strong correlations which develop among themselves and the two replica overlap
at the critical line
Multi-species mean-field spin-glasses. Rigorous results
We study a multi-species spin glass system where the density of each species
is kept fixed at increasing volumes. The model reduces to the
Sherrington-Kirkpatrick one for the single species case. The existence of the
thermodynamic limit is proved for all densities values under a convexity
condition on the interaction. The thermodynamic properties of the model are
investigated and the annealed, the replica symmetric and the replica symmetry
breaking bounds are proved using Guerra's scheme. The annealed approximation is
proved to be exact under a high temperature condition. We show that the replica
symmetric solution has negative entropy at low temperatures. We study the
properties of a suitably defined replica symmetry breaking solution and we
optimise it within a ziggurat ansatz. The generalized order parameter is
described by a Parisi-like partial differential equation.Comment: 17 pages, to appear in Annales Henri Poincar\`
Stochastic thermodynamics of quantum maps with and without equilibrium
We study stochastic thermodynamics for a quantum system of interest whose
dynamics are described by a completely positive trace-preserving (CPTP) map as
a result of its interaction with a thermal bath. We define CPTP maps with
equilibrium as CPTP maps with an invariant state such that the entropy
production due to the action of the map on the invariant state vanishes.
Thermal maps are a subgroup of CPTP maps with equilibrium. In general, for CPTP
maps, the thermodynamic quantities, such as the entropy production or work
performed on the system, depend on the combined state of the system plus its
environment. We show that these quantities can be written in terms of system
properties for maps with equilibrium. The relations that we obtain are valid
for arbitrary coupling strengths between the system and the thermal bath. The
fluctuations of thermodynamic quantities are considered in the framework of a
two-point measurement scheme. We derive the entropy production fluctuation
theorem for general maps and a fluctuation relation for the stochastic work on
a system that starts in the Gibbs state. Some simplifications for the
probability distributions in the case of maps with equilibrium are presented.
We illustrate our results by considering spin 1/2 systems under thermal maps,
non-thermal maps with equilibrium, maps with non-equilibrium steady states and
concatenations of them. Finally, we consider a particular limit in which the
concatenation of maps generates a continuous time evolution in Lindblad form
for the system of interest, and we show that the concept of maps with and
without equilibrium translates into Lindblad equations with and without quantum
detailed balance, respectively. The consequences for the thermodynamic
quantities in this limit are discussed.Comment: 17 pages, 4 figures; new section added, typos correcte
The dark side of centromeres: types, causes and consequences of structural abnormalities implicating centromeric DNA
Centromeres are the chromosomal domains required to ensure faithful transmission of the genome during cell division. They have a central role in preventing aneuploidy, by orchestrating the assembly of several components required for chromosome separation. However, centromeres also adopt a complex structure that makes them susceptible to being sites of chromosome rearrangements. Therefore, preservation of centromere integrity is a difficult, but important task for the cell. In this review, we discuss how centromeres could potentially be a source of genome instability and how centromere aberrations and rearrangements are linked with human diseases such as cancer
- …