Archivio della ricerca dell'UniversitĂ di Modena e Reggio Emiliahttps://iris.unimore.itIl sistema di repository digitale IRIS acquisisce, archivia, indicizza, conserva e rende accessibili prodotti digitali della ricerca.Mon, 29 Nov 2021 06:35:27 GMT2021-11-29T06:35:27Z10121Underdamped commensurate dynamics in a driven Frenkel-Kontorova-type modelhttp://hdl.handle.net/11380/5407Titolo: Underdamped commensurate dynamics in a driven Frenkel-Kontorova-type model
Abstract: The dynamics of a Frenkel-Kontorova chain subject to a substrate potential with a multiple-well structure and driven by an external dc force is studied in the underdamped regime. Making a rational choice among the three inherent length scales characterizing the system allows us to consider the possible formation of commensurate structures during sliding over the complex on-site potential. We comment both on the nature of the particle dynamics in the vicinity of the pinning-depinning transition point, and on the dynamical states displayed during the chain motion at different strengths of the dc driving. Varying the number of particles in the simulations allows us to consider, on a multiple-well substrate, the role played by the coverage variable on the depinning mechanism. The dependence of the minimal force required to initiate the chain motion (static friction) on the ratio of the model interaction strengths is analyzed and compared to the well-known case of the standard Frenkel-Kontorova model, which has only two inherent lengths.
Wed, 01 Jan 2003 00:00:00 GMThttp://hdl.handle.net/11380/54072003-01-01T00:00:00ZFrictional Transition from Superlubric Islands to Pinned Monolayershttp://hdl.handle.net/11380/1080069Titolo: Frictional Transition from Superlubric Islands to Pinned Monolayers
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/11380/10800692015-01-01T00:00:00ZDriven, underdamped Frenkel-Kontorova model on a quasiperiodic substratehttp://hdl.handle.net/11380/6790Titolo: Driven, underdamped Frenkel-Kontorova model on a quasiperiodic substrate
Abstract: We consider the underdamped dynamics of a chain of atoms subject to a de driving force and a quasiperiodic substrate potential. The system has three inherent length scales which we take to be mutually incommensurate. We find that when the length scales are related by the spiral mean (a cubic irrational) there exists a value of the interparticle interaction strength above which the static friction is zero. When the length scales are related by the golden mean (a quadratic irrational) the static friction is always nonzero. From considerations based on the connection of this problem to standard map theory, we postulate that zero static friction is generally possible for incommensurate ratios of the length scales involved. However, when the length scales are quadratic irrationals, or have some commensurability with each other, the static friction will be nonzero for all choices of interaction parameters. We also comment on the nature of the depinning mechanisms and the steady states achieved by the moving chain.
Mon, 01 Jan 2001 00:00:00 GMThttp://hdl.handle.net/11380/67902001-01-01T00:00:00ZSpontaneous pattern formation in driven nonlinear latticeshttp://hdl.handle.net/11380/6882Titolo: Spontaneous pattern formation in driven nonlinear lattices
Abstract: We demonstrate the spontaneous formation of spatial patterns in a damped, ac-driven cubic Klein-Gordon lattice. These patterns are composed of arrays of intrinsic localized modes characteristic for nonlinear lattices. We analyze the modulation instability leading to this spontaneous pattern formation. Our calculation of the modulational instability is applicable in one- and two-dimensional lattices; however, in the analyses of the emerging patterns we concentrate particularly on the two-dimensional case.
Sat, 01 Jan 2000 00:00:00 GMThttp://hdl.handle.net/11380/68822000-01-01T00:00:00ZCommensurate sliding on a multiple-well substrate potentialhttp://hdl.handle.net/11380/305602Titolo: Commensurate sliding on a multiple-well substrate potential
Abstract: In the context of microscopic solid friction phenomena, we study the underdamped dynamics of a Frenkel-Kontorova (FK) chain subject to an external dc force and a substrate potential defined by the sum of two sinusoidal functions with different periodicities. Particularly, focusing on mutually commensurate choices for the three inherent length scales of the system allows us to consider the formation of commensurate structures during sliding over the multiple-well on-site potential. These structures characterize the dynamical states observed during the chain motion at different strengths of the imposed driving. We comment on the nature of the particle dynamics in the vicinity of the pinning-depinning transition point and investigate the role played by the coverage variable on the depinning mechanism. The dependence of the minimal force required to initiate the chain motion (static friction) on the ratio of the model interaction strengths is analyzed and compared to the well-known case of the Frenkel-Kontorova model.
Wed, 01 Jan 2003 00:00:00 GMThttp://hdl.handle.net/11380/3056022003-01-01T00:00:00ZModeling study of microscopic sliding on irregular substrateshttp://hdl.handle.net/11380/22475Titolo: Modeling study of microscopic sliding on irregular substrates
Abstract: In connection with microscopic solid friction phenomena, we study the underdamped dynamics of a driven Frenkelâ€“Kontorova chain subject to a substrate potential defined by the sum of two sinusoidal function with different periodicity.We simulate microscopic sliding over quasiperiodic and multiple-well (periodic) substrates. We comment on thenature of the particle dynamics in the vicinity of the pinningâ€“depinning transition point and consider the role played bythe coverage variable on the depinning mechanism. We also investigate on the different nonlinear excitations formingduring sliding and characterizing the dynamical states observed at different strengths of the imposed driving. Thedependence of the static friction on the ratio of the model interaction strengths is analyzed.
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/11380/224752004-01-01T00:00:00ZThe interaction of intrinsic localized modes in the gap of doped semiconductors with plasmonshttp://hdl.handle.net/11380/305448Titolo: The interaction of intrinsic localized modes in the gap of doped semiconductors with plasmons
Abstract: We present a theoretical investigation of the interaction of intrinsic localized modes with plasmons. The anharmonic localized modes for a ID diatomic lattice are determined using a two-body potential which describes the interactions among particles in a zinc-blende structure material. The localized mode frequency is inside the gap between acoustic and optical phonons. Calculations have been performed for GaN because it has a large phonon gap, can be highly n-doped, and the plasma frequency of free carriers is in the range of phonon and intrinsic localized mode frequencies. To study the coupling we add to the equations of motion an electric field to simulate the plasmon. Solving the system we obtain the dynamical displacements pattern from which we evaluate the total polarization. From the polarization we determine the frequency of the combined mode for which the dielectric function is zero. In this investigation we have analysed both the case of small localized mode amplitudes and the case of larger amplitudes, obtaining different behaviour. In the first case the mixed mode has a frequency above the top of the optical branch, which can be explained in terms of the theory of the harmonic dielectric response of polar lattice vibrations. In the second case the coupled mode exists only for a finite slab, and its frequency is inside the phonon gap.
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/11380/3054482004-01-01T00:00:00ZTransition from smooth sliding to stick-slip motion in a single frictional contacthttp://hdl.handle.net/11380/452145Titolo: Transition from smooth sliding to stick-slip motion in a single frictional contact
Abstract: We show that the transition from smooth sliding to stick-slip motion in a single planar frictional junction always takes place at an atomic-scale relative velocity of the substrates.
Sat, 01 Jan 2005 00:00:00 GMThttp://hdl.handle.net/11380/4521452005-01-01T00:00:00ZHysteretic behaviour in driven Frenkel-Kontorova chains on irregular substrateshttp://hdl.handle.net/11380/4244Titolo: Hysteretic behaviour in driven Frenkel-Kontorova chains on irregular substrates
Abstract: The hysteretic dynamics of a Frenkel-Kontorova chain subject to irregular substrate potentials and driven by an external dc force is studied both in the underdamped and in the overdamped regime at zero temperature. The choice of a rigid external potential defined by the sum of two sinusoidal functions with different periodicity allows us to simulate microscopic sliding over quasiperiodic and multiple-well periodic substrates. We analyse, for different parameter values of the model, the behaviour of the centre of mass average velocity of the chain as a function of an adiabatic increase and decrease of the applied driving. For small damping coefficients (negligible dissipative forces), at a fixed value of the substrate potential amplitude, the width of the hysteresis region is markedly influenced by the chain stiffness. As expected, in the overdamped dynamical regime no hysteresis is observed. We comment on the nature of the dynamical states displayed during the chain motion at different strengths of the dc driving.
Thu, 01 Jan 2004 00:00:00 GMThttp://hdl.handle.net/11380/42442004-01-01T00:00:00ZEnergy localization in pumped systemshttp://hdl.handle.net/11380/6370Titolo: Energy localization in pumped systems
Abstract: Considering a local nonlinear oscillator interacting with a chain of coupled Linear oscillators, we demonstrate that the dynamics of the local oscillator is characterized by a frequency-dependent damping constant, related to the frequency-dependent density of states of the linear modes. Further, we demonstrate how this intrinsic damping provides possibilities for multiple steady states of the nonlinear oscillator, and how these steady states may create local potentials for electrons that are adiabatically coupled with the linear modes. Finally, the implications on coarse-grained mode-ling of hard, softy and biological matter are discussed.
Mon, 01 Jan 2001 00:00:00 GMThttp://hdl.handle.net/11380/63702001-01-01T00:00:00Z