A sheared granular system close to the jamming slips intermittently and with fluctuating velocities. Models for this critical state predict that, if their amplitude is rescaled, short and long slips look identical, in average. Our experiments shows such behaviour for short slips only, whilst longer events displays a breakdown of scaling characterized by friction weakening, amplifying the system instabilities right in the critical state, the most frequent for natural hazards.

** A. Baldassarri, M. A. Annunziata, A. Gnoli, G. Pontuale, A. Petri1
Breakdown of Scaling and Frictionv Weakening in Intermittent Granular
Flow
**
Scientific Reports

** International School of Physics "Enrico Fermi" Summer Course 2-7 July 2018 **

Physics of shallow, intermediate and deep earthquakes - Fundamental of rocks mechanics -

Laboratory experiments -
Inferences from real data - Application to earthquake engineering

*with contributions from *

*K. Aitaro,
R. Archuleta ,
A. Bizzarri,
M. Bouchon,
Y.-T. Chen,
S. Das,
W. S. Ellsworth,
R. Mandariga,
C. Marone,
F. Mulargia,
A. Petri
,A. Schnubnel *

A. Bizzarri, S. Das and A. Petri eds. (SIF-IOS Press)

Here it is found a strict and quantitative correspondence between the dynamics of a two-state Manna model and of a recently introduced Fiber Bundle model effectually describing the propagation of the crack front in a heterogeneous medium. The Manna model itself reveals also able to describe quantitatively the crack dynamical scaling, when supplied of the suited long range redistribution rule. On the other hand the Manna model looks hardly capable to yield the right crack front morphology.

** A. Petri and G. Pontuale Morphology and dynamics in SOC universality classes
**J. Stat. Mech. (2018) 063201

We consider a Lebwohl-Lasher lattice model with nematic directors restricted to point along p planar directions. This XY Lebwohl-Lasher system is the nematic analogue of the standard p-state clock model. We then include chiral interactions, and formulate the problem as a discrete non-linear map on a Cayley tree. The attractors of this map corresponding to the physical solutions, display both uniform and periodic structures, depending on temperature and a parameter of chirality. Sophisticated phase sequences also appear, where the modulation, as a function of model parameters, exhibits a fractal structure, called devilâ€™s staircase

** E. S. Nascimento, A. Petri, S. R. Salinas
Modulated structures in a Lebwohl-Lasher model with chiral interactions
**Physica A: Statistical Mechanics and its Applications

A simple microscopic model based on the Maier-Saupe potential and the Zwanzig approximation to three state shows that thee can be similarities in a certain region of parameters, but elastomers display a much richer phase diagram

** A. Petri and S.R. Salinas Field-induced uniaxial and biaxial nematic phases in the Maier-Saupe-Zwanzig (MSZ) lattice model
**Liquid Crystals, Liquid Crystals

DOI: 10.1080/02678292.2017.1404151

** A. Petri, D.B. Liarte and S.R. Salinas Uniaxial and biaxial structures in the elastic Maier-Saupe model
** Phys. Rev. E

DOI: 10.1103/PhysRevE.97.012705

Adoption of different friction laws for the slip of a mass over a surface only partially affects the main features of the motion. But a rate-and-state law may generate a very long lasting creeping, with almost constant and very low speed, followed by a sudden big slip. Can this be relevant to microtremors?

** A. Bizzarri and A. Petri Single slip dynamics
**
Physics of the Earth and Planetary Interiors,

A plate shearing an interstitial granular medium and driven by an always ongoing spring feels less fricion when only few layers are present. Adding more layers results in an increase of friction, nevertheless the plate slides more often. The ease of slipping is not determined by friction alone?

** M. A. Annunziata, A. Baldassarri, F. Dalton, G. Pontuale and A. Petri Increasing 'ease of sliding' also increasesfriction:when is a lubricant effective?
** J. Phys.: Condens. Matter 28, 134001 (2016)

Each nation exports different products in different amounts. The statistical distribution of the exported volumes can be an indicator of the wealth of a nation. How lognormal is your country?

** M. A. Annunziata, A. Petri, G. Pontuale and A. Zaccaria How log-normal is your country? An analysis of the statistical distribution of the exported volumes of products
** Eur. Phys. J. Special Topics

online https://arxiv.org/abs/1506.03597

The Italian law for the election of Senate utilizes a complex mechanism of awards to improve overall government stability but, as we show, in a significant number of cases, it has the opposite effect of weakening the winning coalition.

**G. Pontuale, F. Dalton, S. Genovese, E. La Nave and A. Petri The electoral system for the Italian Senate: an analogy with deterministic chaos? An analysis via characteristic polynomials
** Ann. Op. Res. 215, 245 (2014)