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Domain structures in ultrathin magnetic films [article]

Paolo Politi
1997 arXiv   pre-print
Domain structures appear in ultrathin magnetic films, if an easy-axis anisotropy, favouring the direction perpendicular to the film, overcomes the shape anisotropy. We will study the nature of the magnetic ground state and how the different parameters influence the domain structure. Both Ising and Heisenberg spins will be considered: in the latter case, a reorientation phase transition may take place. Domains are expected to appear just before such transition. Domain structures at finite
more » ... ture will be described in terms of a two dimensional array of domain walls, whose behaviour resembles a liquid crystal.
arXiv:cond-mat/9712207v1 fatcat:ehbfwvt4hzbvddcszozlejtcgy

Irreversible nucleation in multilayer growth [article]

Paolo Politi, Claudio Castellano
2001 arXiv   pre-print
The epitaxial growth process of a high symmetry surface occurs because adatoms meet and nucleate new islands, that eventually coalesce and complete atomic layers. During multilayer growth, nucleation usually takes place on top of terraces where the geometry of the diffusion process is well defined: We have studied in detail the spatiotemporal distribution of nucleation events and the resulting nucleation rate, a quantity of primary importance to model experimental results and evaluate diffusion
more » ... barriers at step-edges. We provide rigorous results for irreversible nucleation and we assess the limits of mean-field theory (MFT): we show that MFT overestimates the correct result by a factor proportional to the number of times an adatom diffusing on the terrace visits an already visited lattice site. In this report we aim at giving a simple physical account of our results.
arXiv:cond-mat/0107631v1 fatcat:wer3nwkzgzcdnnmyw5cc3c465m

Nonequilibrium phenomena in nonlinear lattices: from slow relaxation to anomalous transport [article]

Stefano Iubini, Stefano Lepri, Roberto Livi, Antonio Politi, Paolo Politi
2019 arXiv   pre-print
This Chapter contains an overview of the effects of nonlinear interactions in selected problems of non-equilibrium statistical mechanics. Most of the emphasis is put on open setups, where energy is exchanged with the environment. With reference to a few models of classical coupled anharmonic oscillators, we review anomalous but general properties such as extremely slow relaxation processes, or non-Fourier heat transport.
arXiv:1911.06017v1 fatcat:yedllsfqqna2pbf33qh35nu3zy

Space symmetries draw elasticity theory [article]

Chaouqi Misbah, Sofia Biagi, Paolo Politi
2013 arXiv   pre-print
The foundation of continuum elasticity theory is based on two general principles: (i) the force felt by a small volume element from its surrounding acts only through its surface (the Cauchy principle, justified by the fact that interactions are of short range and are therefore localized at the boundary); (ii) the stress tensor must be symmetric in order to prevent spontaneous rotation of the material points. These two requirements are presented to be necessary in classical textbooks on
more » ... y theory. By using only basic spatial symmetries it is shown that elastodynamics equations can be derived, for high symmetry crystals (the typical case considered in most textbooks), without evoking any of the two above physical principles.
arXiv:1304.2119v1 fatcat:2daq773jfzerbjkykwed62aa3y

The Three Faces of Populism in Power: Polity, Policies and Politics

Manuela Caiani, Paolo Graziano
2022 Government and Opposition  
Our main contribution is empirical, since – by reflecting on the various articles hosted in the special issue – we assess the impact of populist parties in government on politics, polities and various  ...  Polity The polity dimension usually refers to the institutional settings and constitutional foundations of a system, as well as unwritten rules which form the framework for the political sphere, including  ...  At the same time, they undermine the polity by bypassing institutional checks and balances.  ... 
doi:10.1017/gov.2022.4 fatcat:wn6j7b4marb4nfpyr4nwif6fji

Condensation induced by coupled transport processes [article]

Gabriele Gotti, Stefano Iubini, Paolo Politi
2022 arXiv   pre-print
ACKNOWLEDGMENTS Authors thank Antonio Politi for discussions and Federico Corberi for a critical reading of a first draft of the manuscript.  ... 
arXiv:2208.04419v1 fatcat:ifacbmcf2raxtjq6m3wnr7zqcm

Frozen dynamics of a breather induced by an adiabatic invariant [article]

Antonio Politi, Paolo Politi, Stefano Iubini
2022 arXiv   pre-print
In [Iubini S, Chirondojan L, Oppo G L, Politi A and Politi P 2019 Physical Review Letters 122 084102], it was conjectured that the frozen dynamics of tall breathers is due to the existence of an adiabatic  ... 
arXiv:2201.02529v2 fatcat:53dqss524vgc5j4qwg6w7ynjdq

Steady states of the conserved Kuramoto-Sivashinsky equation [article]

Paolo Politi, Ruggero Vaia
2006 arXiv   pre-print
Recent work on the dynamics of a crystal surface [T.Frisch and A.Verga, Phys. Rev. Lett. 96, 166104 (2006)] has focused the attention on the conserved Kuramoto-Sivashinsky (CKS) equation: ∂_t u = -∂_xx(u+u_xx+u_x^2), which displays coarsening. For a quantitative and qualitative understanding of the dynamics, the analysis of steady states is particularly relevant. In this paper we provide a detailed study of the stationary solutions and their explicit form is given. Periodic configurations form
more » ... n increasing branch in the space wavelength-amplitude (lambda-A), with d(lambda)/dA>0. For large wavelength, lambda=4√(A) and the orbits in phase space tend to a separatrix, which is a parabola. Steady states are found up to an additive constant a, which is set by the dynamics through the conservation law ∂_t =0: a(lambda(t))=lambda^2(t)/48.
arXiv:cond-mat/0609545v1 fatcat:qav4mtgi4fatzoge47kzfz5f5e

Some considerations about reviewing and open-access in scientific publishing [article]

Paolo Politi, Giuseppe Gaeta, Satya N. Majumdar, Antonio Politi, Stefano Ruffo
2022 arXiv   pre-print
The last two contributions concern the Open Access process and are written by Stefano Ruffo (SISSA Trieste) and by the author of this preface (Paolo Politi, CNR Florence).  ...  Antonio Politi It is not clear to me which problems are specific to the Stat Mech area. I am going to argue in general terms. A.  ... 
arXiv:2104.01794v2 fatcat:7lih3k2eqjaynpfeddb4qktjje

Coarsening Dynamics in a Simplified DNLS Model

Stefano Iubini, Antonio Politi, Paolo Politi
2013 Journal of statistical physics  
We investigate the coarsening evolution occurring in a simplified stochastic model of the Discrete NonLinear Schrödinger (DNLS) equation in the so-called negative-temperature region. We provide an explanation of the coarsening exponent n=1/3, by invoking an analogy with a suitable exclusion process. In spite of the equivalence with the exponent observed in other known universality classes, this model is certainly different, in that it refers to a dynamics with two conservation laws.
doi:10.1007/s10955-013-0896-4 fatcat:qhocidxtjjcxdl5ttbi67v3c6i

Different Regimes in the Ehrlich-Schwoebel Instability

Paolo Politi
1997 Journal de Physique I  
doi:10.1051/jp1:1997193 fatcat:4bzhuxganbh4dooisftr4mnrly

Dynamical Freezing of Relaxation to Equilibrium

Stefano Iubini, Liviu Chirondojan, Gian-Luca Oppo, Antonio Politi, Paolo Politi
2019 Physical Review Letters  
We provide evidence of an extremely slow thermalization occurring in the Discrete NonLinear Schr\"odinger (DNLS) model. At variance with many similar processes encountered in statistical mechanics - typically ascribed to the presence of (free) energy barriers - here the slowness has a purely dynamical origin: it is due to the presence of an adiabatic invariant, which freezes the dynamics of a tall breather. Consequently, relaxation proceeds via rare events, where energy is suddenly released
more » ... rds the background. We conjecture that this exponentially slow relaxation is a key ingredient contributing to the non-ergodic behavior recently observed in the negative temperature region of the DNLS equation.
doi:10.1103/physrevlett.122.084102 fatcat:ldafsjhusjaxxiqqntkjfjdvem

Franco Basaglia, 1924–1980

Giovanni de Girolamo, Francesco Barale, Pierluigi Politi, Paolo Fusar-Poli
2008 American Journal of Psychiatry  
doi:10.1176/appi.ajp.2008.07111761 pmid:18676602 fatcat:nvnxyia2z5gsldzhtiq26yjig4

Authors' reply

Matteo Rocchetti, Alberto Sardella, Alessia Avila, Martina Brandizzi, Edgardo Caverzasi, Pierluigi Politi, Stephan Ruhrmann, Philip McGuire, Paolo Fusar-Poli
2016 British Journal of Psychiatry  
Putative high risk for psychosis should not be considered a disorder 3 Bechdolf A, Pukrop R, Kohn D, Tschinkel S, Veith V, Schultze-Lutter F, et al. Subjective quality of life in subjects at risk for a first episode of psychosis: a comparison with first episode schizophrenia patients and healthy controls. Schizophr Res 2005; 79: 137-43. 4 Francey SM, Jackson HJ, Phillips LJ, Wood SJ, Yung AR, McGorry PD. Sustained attention in young people at high risk of psychosis does not predict transition
more » ... psychosis. Schizophr Res 2005; 79: 127-36. 5 Koike S, Takano Y, Iwashiro N, Satomura Y, Suga M, Nagai T, et al. A multimodal approach to investigate biomarkers for psychosis in a clinical setting: the integrative neuroimaging studies in schizophrenia targeting for early intervention and prevention (IN-STEP) project. Schizophr Res 2013; 143: 116-24.
doi:10.1192/bjp.208.2.197a pmid:26834172 fatcat:owjh7uu2kneghluqf7v2hbihbm

Fractal characterization of rain-gauge networks and precipitations: an application in Central Italy [article]

Valerio Capecchi, Alfonso Crisci, Samantha Melani, Marco Morabito, Paolo Politi
2011 arXiv   pre-print
The measuring stations of a geophysical network are often spatially distributed in an inhomogeneous manner. The areal inhomogeneity can be well characterized by the fractal dimension D_H of the network, which is usually smaller than the euclidean dimension of the surface, this latter equal to 2. The resulting dimensional deficit, (2-D_H), is a measure of precipitating events which cannot be detected by the network. The aim of the present study is to estimate the fractal dimension of a
more » ... network in Tuscany (Central Italy) and to relate its dimension to the dimensions of daily rainfall events detected by a mixed satellite/radar methodology. We find that D_H = 1.85, while typical summer precipitations are characterized by a dimension much greater than the dimensional deficit 0.15.
arXiv:1107.1360v1 fatcat:bfsthwnljjfpno6qqlxd6jmq7e
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