arXiv subjects

A. Rosso

Publications and source records attributed to A. Rosso.

11 recordsLinked to original sources

arXiv2024

Adiabatic Light Guide with S-shaped Strips

A light guide is an essential part of many scintillator counters and light collection systems. Our main interest is a light guide for a thin wide scintillator which has high light transmission while converting the area of the light source to the shape of a photo-detector. We propose a variation of the light guide which avoids a 90$\rm ^o$ twist of the strips, reduces the length of the light pipe, and reduces the complexity of production. Detailed Monte Carlo simulation studies have been performed for a 3-strip S-shaped light-guide system.

physics.ins-det↗

arXiv2013

Uniqueness of the thermodynamic limit for driven disordered elastic interfaces

We study the finite size fluctuations at the depinning transition for a one-dimensional elastic interface of size $L$ displacing in a disordered medium of transverse size $M=k L^ζ$ with periodic boundary conditions, where $ζ$ is the depinning roughness exponent and $k$ is a finite aspect ratio parameter. We focus on the crossover from the infinitely narrow ($k\to 0$) to the infinitely wide ($k\to \infty$) medium. We find that at the thermodynamic limit both the value of the critical force and the precise behavior of the velocity-force characteristics are {\it unique} and $k$-independent. We also show that the finite size fluctuations of the critical force (bias and variance) as well as the global width of the interface cross over from a power-law to a logarithm as a function of $k$. Our results are relevant for understanding anisotropic size-effects in force-driven and velocity-driven interfaces.

cond-mat.stat-mech↗

arXiv2013

Numerical Approaches on Driven Elastic Interfaces in Random Media

We discuss the universal dynamics of elastic interfaces in quenched random media. We focus in the relation between the rough geometry and collective transport properties in driven steady-states. Specially devised numerical algorithms allow us to analyze the equilibrium, creep, and depinning regimes of motion in minimal models. The relevance of our results for understanding domain wall experiments is outlined.

cond-mat.dis-nn↗

arXiv2012

Seismic cycles, size of the largest events, and the avalanche size distribution in a model of seismicity

We address several questions on the behavior of a numerical model recently introduced to study seismic phenomena, that includes relaxation in the plates as a key ingredient. We make an analysis of the scaling of the largest events with system size, and show that when parameters are appropriately interpreted, the typical size of the largest events scale as the system size, without the necessity to tune any parameter. Secondly, we show that the temporal activity in the model is inherently non-stationary, and obtain from here justification and support for the concept of a "seismic cycle" in the temporal evolution of seismic activity. Finally, we ask for the reasons that make the model display a realistic value of the decaying exponent $b$ in the Gutenberg-Richter law for the avalanche size distribution. We explain why relaxation induces a systematic increase of $b$ from its value $b\simeq 0.4$ observed in the absence of relaxation. However, we have not been able to justify the actual robustness of the model in displaying a consistent $b$ value around the experimentally observed value $b\simeq 1$.

cond-mat.stat-mech↗

arXiv2008

Thermal Effects in the dynamics of disordered elastic systems

Many seemingly different macroscopic systems (magnets, ferroelectrics, CDW, vortices,..) can be described as generic disordered elastic systems. Understanding their static and dynamics thus poses challenging problems both from the point of view of fundamental physics and of practical applications. Despite important progress many questions remain open. In particular the temperature has drastic effects on the way these systems respond to an external force. We address here the important question of the thermal effect close to depinning, and whether these effects can be understood in the analogy with standard critical phenomena, analogy so useful to understand the zero temperature case. We show that close to the depinning force temperature leads to a rounding of the depinning transition and compute the corresponding exponent. In addition, using a novel algorithm it is possible to study precisely the behavior close to depinning, and to show that the commonly accepted analogy of the depinning with a critical phenomenon does not fully hold, since no divergent lengthscale exists in the steady state properties of the line below the depinning threshold.

cond-mat.dis-nn↗

arXiv2007

Fractional Laplacian in Bounded Domains

The fractional Laplacian operator, $-(-\triangle)^{\fracα{2}}$, appears in a wide class of physical systems, including Lévy flights and stochastic interfaces. In this paper, we provide a discretized version of this operator which is well suited to deal with boundary conditions on a finite interval. The implementation of boundary conditions is justified by appealing to two physical models, namely hopping particles and elastic springs. The eigenvalues and eigenfunctions in a bounded domain are then obtained numerically for different boundary conditions. Some analytical results concerning the structure of the eigenvalues spectrum are also obtained.

cond-mat.stat-mech↗

arXiv2006

Non-equilibrium relaxation of an elastic string in random media

We study the relaxation of an elastic string in a two dimensional pinning landscape using Langevin dynamics simulations. The relaxation of a line, initially flat, is characterized by a growing length, $L(t)$, separating the equilibrated short length scales from the flat long distance geometry that keep memory of the initial condition. We find that, in the long time limit, $L(t)$ has a non--algebraic growth, consistent with thermally activated jumps over barriers with power law scaling, $U(L) \sim L^θ$.

cond-mat.dis-nn↗

arXiv2005

Coulombian Disorder in Periodic Systems

We study the effect of unscreened charged impurities on periodic systems. We show that the long wavelength component of the disorder becomes long ranged and dominates static correlation functions. On the other hand, because of the statistical tilt symmetry, dynamical properties such as pinning remain unaffected. As a concrete example, we focus on the effect of Coulombian disorder generated by charged impurities, on 3D charge density waves with non local elasticity. We calculate the x-ray intensity and find that it is identical to the one produced by thermal fluctuations in a disorder-free smectic-A. We discuss the consequences of these results for experiments.

cond-mat.dis-nn↗

arXiv2005

Dynamics of disordered elastic systems

We review in these notes some dynamical properties of interfaces in random media submitted to an external force. We focuss in particular to the response to a very small force (so called creep motion) and discuss various theoretical aspects of this problem. We consider in details in particular the case of a one dimensional interface (domain wall).

cond-mat.dis-nn↗

arXiv2000

On-site magnetization in open antiferromagnetic chains: a classical analysis versus NMR experiments in a spin-1 compound

The response of an open spin chain with isotropic antiferromagnetic interactions to a uniform magnetic field is studied by classical Monte Carlo simulations. It is observed how the induced on-site magnetization is non uniform, due to the occurrence of edge staggered terms which decay exponentially over a distance equal to the zero field correlation length of the infinite chain. The total magnetic moment associated to each staggered term is found to be about half of the original single-spin magnitude and to decrease as the inverse of temperature (i.e. to behave as a Curie-like moment). The numerical results are compared to recent NMR findings in spinless-doped Y(2)BaNiO(5); the remarkable agreement found shows that, for temperatures above the Haldane gap, the classical approach gives a correct picture of the boundary effects observed in the Heisenberg S=1 chain.

cond-mat.str-el↗

arXiv1999

Superconducting fluctuations and anomalous diamagnetism in underdoped YBa2Cu3O6+x from magnetization and 63Cu NMR-NQR relaxation measurements

Magnetization and 63Cu NMR-NQR relaxation measurements are used to study the superconducting fluctuations in YBa2Cu3O6+x (YBCO) oriented powders. In optimally doped YBCO the fluctuating negative magnetization M_{fl}(H,T) is rather well described by an anisotropic Ginzburg-Landau (GL) functional and the curves M_{fl}/sqrt{H} cross at Tc. In underdoped YBCO, instead, over a wide temperature range an anomalous diamagnetism is observed, stronger than in the optimally doped compound by about an order of magnitude. The field and temperature dependences of M_{fl} cannot be described either by an anisotropic GL functional or on the basis of scaling arguments. The anomalous diamagnetism is more pronounced in samples with a defined order in the Cu(1)O chains. The 63Cu(2) relaxation rate shows little, if any, field dependence in the vicinity of the transition temperature Tc(H=0). It is argued how the results in the underdoped compounds can be accounted for by the presence of charge inhomogeneities, favoured by chains ordering.

cond-mat.str-el↗