[Show abstract][Hide abstract] ABSTRACT: Microscopic self-propelled swimmers capable of autonomous navigation through complex environments provide appealing opportunities for localization, pick-up and delivery of micro-and nanoscopic objects. Inspired by motile cells and bacteria, man-made 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 self-propelled swimmers capable of autonomous navigation through
complex environments provide appealing opportunities for localization, pick-up
and delivery of micro-and nanoscopic objects. Inspired by motile cells and
bacteria, man-made microswimmers have been fabricated, and their motion in
patterned surroundings has been experimentally studied. We propose to use
self-driven 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 quasi-one-dimensional 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 dipole-dipole force are confined in a quasi-one-dimensional channel. The impact of three decisive parameters (the density of particles, the magnetic-moment ratio, and the fraction between the two species) on the transition from disordered phase to crystal-like 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 Newton-Raphson optimization technique, we investigated structural and dynamical properties of two-dimensional binary clusters confined in an external hard-wall 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 ground-state 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 two-dimensional parabolic trap is studied. It is shown that, apart from the well-known center-of-mass 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 two-dimensional (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 two-dimensional 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 "shear-like" and "compression-like" modes, respectively. It is shown that the "shear-like" 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 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.
[Show abstract][Hide abstract] ABSTRACT: The HT-7U 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 MCNP-4C and the latest version of the Fusion Evaluated Nuclear Data Library (FENDL-2) based on the three-dimensional 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 double-wall-structured 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 design of the radiation shield and safety system for the HT-7U 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 HT-7U device. The safety system has the advantages of multi-master protocol, real-time capability, error correction, long communication distance and high noise immunity etc.
[Show abstract][Hide abstract] ABSTRACT: The configurational properties of two-dimensional clusters of charged dust particles in dusty plasma interacting with each other via a model potential with a short-range repulsion and a long-range 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.
Physica Scripta 05/2003; 27(5). DOI:10.1238/Physica.Regular.067a00439 · 1.13 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The static and dynamical properties of two-dimensional 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 ground-state configuration and the position of the geometry induced defects are investigated as a function of the inter-particle interaction (Coulomb, dipole, logarithmic and screened Coulomb). The eigenmodes are investigated and the corresponding divergence and rotor are calculated which describe the `shearlike' and `compression-like' modes, respectively. The melting behaviour is found to be strongly influenced by the inter-particle interaction potential: a small cluster with a short-range interaction melts earlier than one with long-range 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.
New Journal of Physics 03/2003; 5(1):23. DOI:10.1088/1367-2630/5/1/323 · 3.56 Impact Factor
[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 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.
[Show abstract][Hide abstract] ABSTRACT: 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.