PubMed Health⌕ Search

Biomedical subjects

V Bortolani

Publications and source records attributed to V Bortolani.

18 recordsLinked to original sources
PubMed2004

Corrugating and anticorrugating static interactions in helium-atom scattering from metal surfaces.

We perform a density-functional-theory calculation of the static repulsive potential of He scattering off a noble and a simple metal surface. The classical turning point of He on Cu(111) is found to be closer to the metal when the adatom is at top than at bridge site (anticorrugating effect). The potential of He on Al(111) is instead corrugated. By comparing the results of the two systems, we conclude that the He-metal anticorrugating effect occurs when the kinetic energy difference for He at top and bridge sites is larger than the electrostatic one, and an induced localized dipole on He is formed.

Journal Article↗
PubMed2003

Underdamped commensurate dynamics in a driven Frenkel-Kontorova-type model.

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.

Journal Article↗
PubMed2000

Driven, underdamped Frenkel-Kontorova model on a quasiperiodic substrate.

We consider the underdamped dynamics of a chain of atoms subject to a dc 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.

Journal Article↗
PubMed2000

Spontaneous pattern formation in driven nonlinear lattices

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.

Journal Article↗