1,721,023 research outputs found
COLLOIDAL FRICTION Kinks in motion
No full textThe ability of laser interference potentials to trap and control colloidal particles opens up a new potential area of
‘toy systems’ displaying real physics. A beautiful example is the study of friction between colloidal crystals and a
variety of artificially created surface potentials
Hysteretic behaviour in driven Frenkel-Kontorova chains on irregular substrates
No full textThe 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
Role of substrate geometry in sliding friction
No full textVia a Frenkel-Kontorova (FK) model approach, we study, in the context of solid friction phenomena, the role of the substrate potential geometry on the underdamped dynamics of a chain of interacting atoms. The choice of an on-site potential defined by the sum of two sinusoidal functions with different periodicity allows us to simulate microscopic sliding over simply periodic, multiple-well periodic and quasiperiodic substrates. We analyse the mobility-force characteristics and the related static friction, commenting on the nature of the particle dynamics in the vicinity of the pinning-depinning transition point and considering the role played by the coverage variable on the depinning mechanism. For the quasiperiodic cases, we also examine the hysteretic behaviour of the chain mobility as a function of the adiabatically varying force at zero temperature. For multiple-well periodic potentials, we observe the possible formation of commensurate dynamical structures during sliding
Anharmonic effects in a finite Frenkel-Kontorova type chain
No full textThe features of the ground state and the phonon frequency spectrum of a finite Frenkel-Kontorova type model are investigated in presence of quartic anharmonic nearest-neighbor interactions. The different computational techniques used allow us to determine with great accuracy the critical parameter for the ground-state symmetry breaking transition, showing its dependence on the strength of the interatomic anharmonicity introduced. The phonon gap. the linearized vibrational modes and their parity are also studied in the vicinity of the transition point. (C) 2002 Elsevier Science B.V. All rights reserved
Underdamped commensurate dynamics in a driven Frenkel-Kontorova-type model
No full textThe 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
Spontaneous pattern formation in driven nonlinear lattices
No full textWe 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
Modeling study of microscopic sliding on irregular substrates
No full textIn connection with microscopic solid friction phenomena, we study the underdamped dynamics of a driven Frenkel–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 pinning–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
The interaction of intrinsic localized modes in the gap of doped semiconductors with plasmons
No full textWe 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
Energy localization in pumped systems
No full textConsidering 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
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