Publications (15)28.13 Total impact
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ABSTRACT: Microscopic selfpropelled swimmers capable of autonomous navigation through complex environments provide appealing opportunities for localization, pickup and delivery of microand nanoscopic objects. Inspired by motile cells and bacteria, manmade microswimmers have been created, and their motion was studied experimentally in patterned surroundings. We propose to use the microswimmers  Janus spheres illuminated by light  as "driving agents" that move through a binary mixture of colloidal particles. We demonstrate that binary mixtures can be effectively separated in this way. We analyze different regimes of separation. Our finding could be of use for various biological and medical applications.  [Show abstract] [Hide abstract]
ABSTRACT: Microscopic selfpropelled swimmers capable of autonomous navigation through complex environments provide appealing opportunities for localization, pickup and delivery of microand nanoscopic objects. Inspired by motile cells and bacteria, manmade microswimmers have been fabricated, and their motion in patterned surroundings has been experimentally studied. We propose to use selfdriven artificial microswimmers for separation of binary mixtures of colloids. We revealed different regimes of separation including one with a velocity inversion. Our finding could be of use for various biological and medical applications.  [Show abstract] [Hide abstract]
ABSTRACT: The structural properties of a binary colloidal quasionedimensional system confined in a narrow channel are investigated through modified Monte Carlo simulations. Two species of particles with different magnetic moment interact through a repulsive dipoledipole force are confined in a quasionedimensional channel. The impact of three decisive parameters (the density of particles, the magneticmoment ratio, and the fraction between the two species) on the transition from disordered phase to crystallike phases and the transitions among the different mixed phases are summarized in a phase diagram.  [Show abstract] [Hide abstract]
ABSTRACT: Within the Monte Carlo formalism supplemented by the modified NewtonRaphson optimization technique, we investigated structural and dynamical properties of twodimensional binary clusters confined in an external hardwall potential. Two species of differently charged classical particles, interacting through the repulsive Coulomb force are confined in the cluster. Subtle changes in the energy landscape and the stable cluster configurations are investigated as a function of the total number of particles and the relative number of each of the two particle species. The excitation spectrum and the normal modes corresponding to the groundstate configuration of the system are discussed, and the lowest nonzero eigenfrequency as a measure of the stability of the cluster is analyzed. The influence of the particle mass on the eigenfrequencies and eigenmodes are studied, i.e., we study a binary system of particles with different charge and different mass. Several unique features distinct from a monodisperse system are obtained.  [Show abstract] [Hide abstract]
ABSTRACT: The frequency spectrum of a system of classical charged particles interacting through a Coulomb repulsive potential and which are confined in a twodimensional parabolic trap is studied. It is shown that, apart from the wellknown centerofmass and breathing modes, which are independent of the number of particles in the cluster, there are more "universal" modes whose frequencies depend only slightly on the number of particles. To understand these modes the spectrum of excitations as a function of the number of particles is compared with the spectrum obtained in the hydrodynamic approach. The modes are classified according to their averaged vorticity and it is shown that these "universal" modes have the smallest vorticity and follow the hydrodynamic behavior.  [Show abstract] [Hide abstract]
ABSTRACT: The distortion due to a fixed point impurity with variable charge placed in the center of a classical harmonically confined twodimensional (2D) large Coulomb cluster is studied. We find that the net topological charge (N()N+ ) of the system is always equal to six independent of the position and charge of the impurity. In comparison with a 2D cluster without impurity charge, only the breathing mode remains unchanged. The screening length is found to be a highly nonlinear function of the impurity charge. For values of the impurity charge smaller than the charge of the other particles, the system has almost the same screening strength. When the impurity charge is larger, the screening length is strongly enhanced. This result can be explained by the competition between the different forces active in the system.  [Show abstract] [Hide abstract]
ABSTRACT: The magnetic field dependence of the normal mode spectra of twodimensional finite clusters of complex plasmas which are confined by an external harmonic potential is presented. The dependence of the normal mode spectrum as a function of a perpendicular magnetic field is discussed. The nature of the eigenmodes is investigated and the corresponding divergence and rotor were calculated which describe the "shearlike" and "compressionlike" modes, respectively. It is shown that the "shearlike" character of the modes is increased due to the presence of the magnetic field.  [Show abstract] [Hide abstract]
ABSTRACT: The structural and dynamical properties of twodimensional (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 groundstate configuration is investigated as a function of the interparticle interaction (Coulomb, dipole, logarithmic, and screened Coulomb). The excitation spectrum corresponding to the groundstate 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.  [Show abstract] [Hide abstract]
ABSTRACT: The design of the radiation shield and safety system for the HT7U fusion experimental device is presented in this contribution. An inner shield and an outer shield are considered in the shield design. Calculations and analyses have been done using 3D MCNP/4C models for the neutron spectrum and with the inventory code FISPACT for activation calculation in order to estimate the dose rate to workers after one pulse operation of the device. In addition, a computer system for radiation protection and control based on Controller Area Network has been developed in order to protect staff and publics from the radiation of neutrons and γ during and after the operation of the HT7U device. The safety system has the advantages of multimaster protocol, realtime capability, error correction, long communication distance and high noise immunity etc.  [Show abstract] [Hide abstract]
ABSTRACT: The HT7U superconducting tokamak will generate neutrons at a rate of the order of 1015 per second during the D–D operation with long pulse up to 1000 s. Nuclear heat in the Toroidal Field (TF) and Poloidal Field (PF) coils have been estimated by using the Monte Carlo particle transport code MCNP4C and the latest version of the Fusion Evaluated Nuclear Data Library (FENDL2) based on the threedimensional geometrical configuration. The calculations show that the nuclear heat in the coils originates ∼10% from neutron energy deposition and ∼90% from induced gamma energy deposition. To reduce the nuclear heat in the superconducting magnets of the TF and PF coils, a doublewallstructured vacuum vessel (VV) with the boronated water layer of thickness of 5 cm is designed to shield against neutron irradiation.  [Show abstract] [Hide abstract]
ABSTRACT: The configurational properties of twodimensional clusters of charged dust particles in dusty plasma interacting with each other via a model potential with a shortrange repulsion and a longrange attraction are investigated through the Monte Carlo simulation technique. The particles are confined by a harmonic potential. For the small number of particles, a hexagonal structure of the ground state changes into a shell configuration with increasing value of the attraction parameter : For larger clusters, the increased attraction changes the defect locations and more particles energetically suit in the center of the cluster. 
Article: Structural, dynamical and melting properties of twodimensional clusters of complex plasmas
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ABSTRACT: The static and dynamical properties of twodimensional mesoscopic clusters of equally charged classical particles are investigated through the Monte Carlo simulation technique. The particles are confined by an external harmonic potential. The groundstate configuration and the position of the geometry induced defects are investigated as a function of the interparticle interaction (Coulomb, dipole, logarithmic and screened Coulomb). The eigenmodes are investigated and the corresponding divergence and rotor are calculated which describe the `shearlike' and `compressionlike' modes, respectively. The melting behaviour is found to be strongly influenced by the interparticle interaction potential: a small cluster with a shortrange interaction melts earlier than one with longrange interaction. The melting temperature is related to the energy barriers between the ground state and the metastable states. For larger clusters, the melting scenario changes and is strongly influenced by the location of the topological defects.  [Show abstract] [Hide abstract]
ABSTRACT: The configurational and melting properties of large twodimensional (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 hexagonalshaped 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.  [Show abstract] [Hide abstract]
ABSTRACT: 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 using Monte Carlo (MC) simulations. 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 formation of a hexagonal lattice in the center which is the groundstate for an infinite 2D system, and the effect of the confinement which wants to impose its circular symmetry on the outer edge. In the transition region defects appear at the six corners of the hexagonal‐shaped inner domain. The melting of this cluster is found to be strongly related to the local topological structure. Our results clearly show that the melting starts near the geometry induced defects and that three melting temperatures can be obtained. © 2002 American Institute of Physics  [Show abstract] [Hide abstract]
ABSTRACT: Structural and static properties of a classical twodimensional 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 wellknown 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 groundstate configuration on the functional form of the interparticle interaction and on the confinement potential is also investigated.
Publication Stats
256  Citations  
28.13  Total Impact Points  
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Institutions

20022006

University of Antwerp
 Departement Fysica
Antwerpen, VLG, Belgium
