arXiv subjects

M. Romero-Bastida

Publications and source records attributed to M. Romero-Bastida.

15 recordsLinked to original sources

arXiv2024

Thermal rectification in segmented Frenkel-Kontorova lattices with asymmetric next-nearest-neighbor interactions

In this work we conduct an extensive study of the asymmetric heat flow, i.e. thermal rectification, present in the two-segment Frenkel Kontorova model with both nearest-neighbor (NN) and next-nearest-neighbor (NNN) interactions. We have considered systems with both high and low asymmetry and determined that, in the weak-coupling limit, thermal rectification is larger when NNN interactions are relevant. The behavior of the heat fluxes as a function of the coupling strength between the two segments is largely consistent with a well-defined rectification for larger system sizes. The local heat fluxes present a very different behavior for systems with high and low asymmetry. The results of this work may help in the design of molecular bridges, which have recently been shown to be able to function as thermal rectification devices.

cond-mat.stat-mech↗

arXiv2024

Effect of external potential on the energy transport in harmonically driven segmented Frenkel-Kontorova lattices

Thermal resonance, that is, the heat flux obtained by means of a periodic external driving, offers the possibility of controlling heat flux in nanoscale devices suitable for power generation, cooling, and thermoelectrics among others. In this work we study the effect of the onsite potential period on the thermal resonance phenomenon present in a one-dimensional system composed of two dissimilar Frenkel-Kontorova lattices connected by a time-modulated coupling and in contact with two heat reservoirs operating at different temperature by means of molecular dynamics simulations. When the periods of the onsite potential on both sides of the system are equal the maximum resonance is obtained for the lowest considered value of the period. For highly structurally asymmetric lattices the heat flux toward the cold reservoir is maximized, and asymmetric periods of the onsite potential afford an extra way to control the magnitude of the heat fluxes in each side of the system. Our results highlight the importance of the substrate structure on thermal resonance and could inspire further developments in designing thermal devices.

cond-mat.stat-mech↗

arXiv2022

Thermal resonance in harmonically driven segmented Frenkel-Kontorova lattices with next-nearest-neighbor interactions

Problems of heat transport are ubiquitous to various technologies such as power generation, cooling, electronics, and thermoelectrics. Within this context it is natural that external heat flux control on nanoscale devices became an appealing strategy that has been explored in recent years. In this work we study the thermal resonance phenomenon, i.e., the maximum heat flux obtained by means of an external periodic driving, of a one-dimensional system composed of two dissimilar Frenkel-Kontorva lattices with both nearest-neighbor (NN) and next-nearest-neighbor (NNN) interactions connected by time-modulated NN and NNN couplings in contact with two heat reservoirs operating at different temperature. We study the effect of the NNN interactions on the various heat transport regimes afforded by the structural modifications that can be made on the model. The dependence of the thermal resonance on the system size is studied as well. Our results show that, despite the increased connectivity of both sides afforded by the NNN interactions, the overlap of the phonon bands of both parts of the system still determines the frequency range wherewith thermal resonance emerges.

cond-mat.stat-mech↗

arXiv2021

Thermal rectification in three-dimensional mass-graded anharmonic oscillator lattices

In this work we study the thermal rectification efficiency, i.e., asymmetric heat flow, of a three-dimensional mass-graded anharmonic lattice of length $N$ and width $W$ by means of nonequilibrium molecular dynamics simulations. The obtained rectification, which is of the same order of magnitude as that of the corresponding one-dimensional lattice, saturates at low values of the aspect ratio $W/N$, consistent with the already known behavior of the corresponding heat fluxes of the homogeneous system under analogous conditions. The maximum rectification is obtained in the temperature range wherein no rectification could be obtained in other one-dimensional systems, as well as in the corresponding one-dimensional instance of the model studied herein.

cond-mat.stat-mech↗

arXiv2021

Thermal rectification in oscillator lattices with a ballistic spacer and next nearest-neighbor interactions

In this work we study the asymmetric heat flow, i.e., thermal rectification, of a one-dimensional, mass-graded system consisting of acoupled harmonic oscillator lattice (ballistic spacer) and two diffusive leads attached to the boundaries of the former with both nearest-neighbor and next-nearest-neighbor (NNN) interactions. The latter enhance the rectification properties of the system and specially its independence on system size. The system presents a maximum rectification efficiency for a very precise value of the parameter that controls the coupling strength of the NNN interactions that depend on the temperature range wherein the device operates. The origin of this maximum value is the asymmetric local heat flow response corresponding to the NNN contribution at both sides of the lighter mass-loaded diffusive lead as quantified by the spectral properties. Upon variation of the system's parameters the performance of the device is always enhanced in the presence of NNN interactions.

cond-mat.stat-mech↗

arXiv2020

Energy transport in harmonically driven segmented Frenkel-Kontorova lattices

In this work we study the energy transport in a one-dimensional system composed of two dissimilar Frenkel-Kontorova lattices connected by a time-modulated coupling and in contact with two heat reservoirs operating at different temperature by means of molecular dynamics simulations. There is a value of the driving frequency at which the heat flux takes its maximum value, a phenomenon termed as thermal resonance. Structural modifications in the lattice strongly alter the way in which the external driving interacts with the phonon bands. The overlap of the latter in the harmonic regime of the model determine the frequency range wherein resonance emerges. Parameter dependencies by which the incoming heat flux can be directed to either of the heat reservoirs are examined as well. Our results may be conductive to further developments in designing thermal devices.

cond-mat.stat-mech↗

arXiv2020

Efficient harmonic oscillator chain energy harvester driven by colored noise

We study the performance of an electromechanical harmonic oscillator chain as an energy harvester to extract power from finite-bandwidth ambient random vibrations, which are modelled by colored noise. The proposed device is numerically simulated and its performance assessed by means of the net electrical power generated and its efficiency in converting the external noise-supplied power into electrical power. Our main result is a much enhanced performance, both in the net electrical power delivered and in efficiency, of the harmonic chain with respect to the popular single oscillator resonator. Our numerical findings are explained by means of an analytical approximation, in excellent agreement with numerics.

cond-mat.stat-mech↗

arXiv2014

Size effects on thermal rectification in mass-graded anharmonic lattices

In this work we study the thermal rectification efficiency of a one-dimensional mass-graded anharmonic oscillator lattice at large system sizes. A modest increase in rectification is observed. When the magnitude of the mass gradient scales with the system size, the aforementioned effect increases substantially. This result can be unmistakeably attributed to an asymmetry in the local temperature profile obtained for the employed parameter values.

cond-mat.stat-mech↗

arXiv2012

Covariant hydrodynamic Lyapunov modes and strong stochasticity threshold in Hamiltonian lattices

We scrutinize the reliability of covariant and Gram-Schmidt Lyapunov vectors for capturing hydrodynamic Lyapunov modes (HLMs) in one-dimensional Hamiltonian lattices. We show that,in contrast with previous claims, HLMs do exist for any energy density, so that strong chaos is not essential for the appearance of genuine (covariant) HLMs. In contrast, Gram-Schmidt Lyapunov vectors lead to misleading results concerning the existence of HLMs in the case of weak chaos.

nlin.CD↗

arXiv2011

Efficient time series detection of the strong stochasticity threshold in Fermi-Pasta-Ulam oscillator lattices

In this work we study the possibility of detecting the so-called strong stochasticity threshold, i.e. the transition between weak and strong chaos as the energy density of the system is increased, in anharmonic oscillator chains by means of the 0-1 test for chaos. We compare the result of the aforementioned methodology with the scaling behavior of the largest Lyapunov exponent computed by means of tangent space dynamics, that has so far been the most reliable method available to detect the strong stochasticity threshold. We find that indeed the 0-1 test can perform the detection in the range of energy density values studied. Furthermore, we determined that conventional nonlinear time series analysis methods fail to properly compute the largest Lyapounov exponent even for very large data sets, whereas the computational effort of the 0-1 test remains the same in the whole range of values of the energy density considered with moderate size time series. Therefore, our results show that, for a qualitative probing of phase space, the 0-1 test can be an effective tool if its limitations are properly taken into account.

nlin.CD↗

arXiv2010

Structure of characteristic Lyapunov vectors in anharmonic Hamiltonian lattices

In this work we perform a detailed study of the scaling properties of Lyapunov vectors (LVs) for two different one-dimensional Hamiltonian lattices: the Fermi-Pasta-Ulam and $Φ^4$ models. In this case, characteristic (also called covariant) LVs exhibit qualitative similarities with those of dissipative lattices but the scaling exponents are different and seemingly nonuniversal. In contrast, backward LVs (obtained via Gram-Schmidt orthonormalizations) present approximately the same scaling exponent in all cases, suggesting it is an artificial exponent produced by the imposed orthogonality of these vectors. We are able to compute characteristic LVs in large systems thanks to a `bit reversible' algorithm, which completely obviates computer memory limitations.

nlin.CD↗

arXiv2008

Lyapunov modes in three-dimensional Lennard-Jones fluids

Recent studies on the phase-space dynamics of a one-dimensional Lennard-Jones fluid reveal the existence of regular collective perturbations associated with the smallest positive Lyapunov exponents of the system, called hydrodynamic Lyapunov modes, which previously could only be identified in hard-core fluids. In this work we present a systematic study of the Lyapunov exponents and Lyapunov vectors, i.e. perturbations along each direction of phase space, of a three-dimensional Lennard-Jones fluid. By performing the Fourier transform of the spatial density of the coordinate part of the Lyapunov vector components and then time-averaging this result we find convincing signatures of longitudinal modes, with inconclusive evidence of transverse modes for all studied densities. Furthermore, the longitudinal modes can be more clearly identified for the higher density values. Thus, according to our results, the mixing of modes induced both by the dynamics and the dimensionality induce a hitherto unknown type of order in the tangent space of the model herein studied at high density values.

nlin.CD↗

arXiv2005

Macroscopic evidence of microscopic dynamics in the Fermi-Pasta-Ulam oscillator chain from nonlinear time series analysis

The problem of detecting specific features of microscopic dynamics in the macroscopic behavior of a many-degrees-of-freedom system is investigated by analyzing the position and momentum time series of a heavy impurity embedded in a chain of nearest-neighbor anharmonic Fermi-Pasta-Ulam oscillators. Results obtained in a previous work [M. Romero-Bastida, Phys. Rev. E {\bf69}, 056204 (2004)] suggest that the impurity does not contribute significantly to the dynamics of the chain and can be considered as a probe for the dynamics of the system to which the impurity is coupled. The ($r,τ$) entropy, which measures the amount of information generated by unit time at different scales $τ$ of time and $r$ of the observable, is numerically computed by methods of nonlinear time-series analysis using the position and momentum signals of the heavy impurity for various values of the energy density $ε$ (energy per degree of freedom) of the system and some values of the impurity mass $M$. Results obtained from these two time series are compared and discussed.

nlin.CD↗

arXiv2004

Macroscopic detection of the strong stochasticity threshold in Fermi-Pasta-Ulam chains of oscillators

The largest Lyapunov exponent of a system composed by a heavy impurity embedded in a chain of anharmonic nearest-neighbor Fermi-Pasta-Ulam oscillators is numerically computed for various values of the impurity mass $M$. A crossover between weak and strong chaos is obtained at the same value $ε_{_T}$ of the energy density $ε$ (energy per degree of freedom) for all the considered values of the impurity mass $M$. The threshold $\epsi lon_{_T}$ coincides with the value of the energy density $ε$ at which a change of scaling of the relaxation time of the momentum autocorrelation function of the impurity ocurrs and that was obtained in a previous work ~[M. Romero-Bastida and E. Braun, Phys. Rev. E {\bf65}, 036228 (2002)]. The complete Lyapunov spectrum does not depend significantly on the impurity mass $M$. These results suggest that the impurity does not contribute significantly to the dynamical instability (chaos) of the chain and can be considered as a probe for the dynamics of the system to which the impurity is coupled. Finally, it is shown that the Kolmogorov-Sinai entropy of the chain has a crossover from weak to strong chaos at the same value of the energy density that the crossover value $ε_{_T}$ of largest Lyapunov exponent. Implications of this result are discussed.

nlin.CD↗

arXiv2002

Microscopic chaos from Brownian motion in a one-dimensional anharmonic oscillator chain

The problem of relating microscopic chaos to macroscopic behavior in a many-degrees-of-freedom system is numerically investigated by analyzing statistical properties associated to the position and momentum of a heavy impurity embedded in a chain of nearest-neighbor anharmonic Fermi-Pasta-Ulam oscillators. For this model we have found that the behavior of the relaxation time of the momentum autocorrelation function of the impurity is different depending on the dynamical regime (either regular or chaotic) of the lattice.

nlin.CD↗