Biomedical subjects

F M Peeters

Publications and source records attributed to F M Peeters.

24 records · Page 2Linked to original sources

PubMed2004

Structure and spectrum of two-dimensional clusters confined in a hard wall potential.

The structural and dynamical properties of two-dimensional (2D) clusters of equally charged classical particles, which are confined in an external hard wall potential, are investigated through the Monte Carlo simulation technique. The ground-state configuration is investigated as a function of the interparticle interaction (Coulomb, dipole, logarithmic, and screened Coulomb). The excitation spectrum corresponding to the ground-state configuration of the system is discussed. The eigenmodes are investigated and the corresponding divergence and rotor are calculated, which indicates the "shearlike" and "compressionlike" aspects of the different modes. Both small and large clusters are considered.

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PubMed2003

Normal mode spectra of two-dimensional classical atoms confined by a Coulomb potential.

The normal mode spectra of two-dimensional finite clusters of charged particles (-e) confined by a Coulomb potential resulting from a displaced positive charge Ze are obtained. This is a classical two-dimensional model system for atoms. We obtain the frequencies of the normal modes as a function of the confinement charge Z and the number of particles N. The analysis of the lowest normal mode frequency reveals a good agreement with the experimental results obtained in a system with screened interaction between charged particles. The dependence of the normal mode spectra as a function of a perpendicular magnetic field is also discussed and we found that the shear-like character of the modes is enhanced in the presence of the magnetic field. For large values of the magnetic fields the normal modes fall into two bands, a low frequency band with frequency approximately 1/omega(c) and a high frequency band with frequency approximately omega(c).

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PubMed2003

Current-voltage characteristics of quasi-one-dimensional superconductors: an S-shaped curve in the constant voltage regime.

Applying a constant voltage to superconducting nanowires we find that its I-V characteristic exhibits an unusual S behavior. This behavior is the direct consequence of the dynamics of the superconducting condensate and of the existence of two different critical currents: j(c2) at which the pure superconducting state becomes unstable and j(c1)<j(c2) at which the phase-slip state is realized in the system.

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PubMed2003

Structure and correlations in two-dimensional classical artificial atoms confined by a Coulomb potential.

The ordering of N equally charged particles (-e) moving in two dimensions and confined by a Coulomb potential, resulting from a displaced positive charge Ze is discussed. This is a classical model system for atoms. We obtain the configurations of charged particles which, depending on the value of N and Z, may result in ring structures, hexagonal-type configurations, and for N/Z approximately 1 in an inner structure of particles which is separated by an outer ring of particles. For N/Z<<1, the Hamiltonian of the parabolic confinement case is recovered. For N/Z approximately 1, the configurations are very different from those found in the case of a parabolic confinement potential. A hydrodynamic analysis is presented in order to highlight the correlations effects.

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PubMed2003

Topological defects and nonhomogeneous melting of large two-dimensional Coulomb clusters.

The configurational and melting properties of large two-dimensional (2D) clusters of charged classical particles interacting with each other via the Coulomb potential are investigated through the Monte Carlo simulation technique. The particles are confined by a harmonic potential. For a large number of particles in the cluster (N>150), the configuration is determined by two competing effects, namely, the fact that in the center a hexagonal lattice is formed, which is the groundstate for an infinite 2D system, and the confinement that imposes its circular symmetry on the outer edge. As a result, a hexagonal Wigner lattice is formed in the central area while at the border of the cluster the particles are arranged in rings. In the transition region defects appear as dislocations and disclinations at the six corners of the hexagonal-shaped inner domain. Many different arrangements and types of defects are possible as metastable configurations with a slightly higher energy. The particle motion is found to be strongly related to the topological structure. Our results clearly show that the melting of the clusters starts near the geometry induced defects, and that three different melting temperatures can be defined corresponding to the melting of different regions in the cluster.

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PubMed2002

Transition between ground state and metastable states in classical two-dimensional atoms.

Structural and static properties of a classical two-dimensional system consisting of a finite number of charged particles that are laterally confined by a parabolic potential are investigated by Monte Carlo simulations and the Newton optimization technique. This system is the classical analog of the well-known quantum dot problem. The energies and configurations of the ground and all metastable states are obtained. In order to investigate the barriers and the transitions between the ground and all metastable states we first locate the saddle points between them, then by walking downhill from the saddle point to the different minima, we find the path in configurational space from the ground state to the metastable states, from which the geometric properties of the energy landscape are obtained. The sensitivity of the ground-state configuration on the functional form of the interparticle interaction and on the confinement potential is also investigated.

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