Particle-field Interaction Research Articles

Classical local SU(3) gauge invariance in Weyl 2-spinor language and quark–gluon plasma equations of motion

In a new classical Weyl 2-spinor approach to non abelian gauge theories, starting with the U(1) gauge group in a previous work, we study now the SU(3) case corresponding to quarks (antiquarks) interacting with color fields. The principal difference with the conventional approach is that particle-field interactions are not described by means of potentials but by the field strength magnitudes. Some analytical expressions showing similarities with electrodynamics are obtained. Classical equations that describe the behavior of quarks under gluon fields might be in principle applied to the quark–gluon plasma phase existing during the first instants of the Universe.

A Stokesian dynamics approach for simulation of magnetic particle suspensions

The dynamic behaviour of μm-scale ferromagnetic particles in suspension is of interest for various mineral beneficiation processes. It is, however, difficult to experimentally study such processes at the particle-level. In these instances it can be advantageous to resort to suitable particle simulation methods.Stokesian dynamics is a mesh-free numerical technique developed for suspensions of nm to mm size particles. The method inherently considers hydrodynamic interactions, but additional interaction models can be included depending on the system under investigation. We here present a Stokesian dynamics (SD) implementation, which allows for simulation of the motion of suspended magnetic particles in presence of an external magnetic field. The magnetic interaction model includes particle-field interactions as well as pairwise interactions between magnetised particles.Simulations are compared with experiments using a laboratory-scale flow cell. The method is shown to be realistic for studying ferromagnetic suspensions in mineral processing applications, and can be useful in understanding and predicting the efficiency of mineral separation processes.

Monte-Carlo approach to particle-field interactions and the kinetics of the chiral phase transition

The kinetics of the chiral phase transition is studied within a linear quark-meson-σ model, using a Monte-Carlo approach to semiclassical particle-field dynamics. The meson fields are described on the mean-field level and quarks and antiquarks as ensembles of test particles. Collisions between quarks and antiquarks as well as the annihilation to σ mesons and the decay of σ mesons is treated, using the corresponding transition-matrix elements from the underlying quantum field theory, obeying strictly the rule of detailed balance and energy-momentum conservation. The approach allows to study fluctuations without making ad hoc assumptions concerning the statistical nature of the random process as necessary in Langevin-Fokker-Planck frameworks.

Brownian dynamics simulations with spin Brownian motion on the negative magneto-rheological effect of a rod-like hematite particle suspension

We have investigated the behaviour of a suspension of magnetic rod-like hematite particles in a simple shear flow with the addition of an applied magnetic field. A significant feature of the present hematite particle suspension is the fact that the magnetic moment of the hematite particle lies normal to the particle-axis direction. From simulations, we have attempted to clarify the dependence of the negative magneto-rheological effect on the particle aggregation and orientational distribution of particles. The present Brownian dynamics method has a significant advantage in that it takes into account the spin rotational Brownian motion about the particle axis in addition to the ordinary translational and rotational Brownian motion. The net viscosity is decomposed into three components and discussed at a deeper level and in detail: these three viscosity components arise from (1) the torque due to the magnetic particle–field interaction, (2) the torque and (3) the force due to the interaction between particles. It is found that a slight change in the orientational distribution has a significant influence on the negative magneto-rheological effect. In a relatively dense suspension, the viscosity components arising from an applied magnetic field and the interaction between particles come to change rapidly for a certain strength of the magnetic particle–particle interaction, which is due to the onset of the formation of raft-like clusters.

Comparison between kinetic-ballooning-mode-driven turbulence and ion-temperature-gradient-driven turbulence

Electromagnetic turbulence driven by kinetic ballooning modes (KBMs) in high-β plasma is investigated based on the local gyrokinetic model. Analysis of turbulent fluxes, norms, and phases of fluctuations shows that KBM turbulence gives narrower spectra and smaller phase factors than those in ion-temperature-gradient (ITG)-driven turbulence. This leads to the smaller transport fluxes in KBM turbulence than those in ITG turbulence even when they have similar linear growth rates. From the analysis of the entropy balance relation, it is found that the entropy transfer from ions to electrons through the field-particle interactions mainly drives electron perturbations, which creates radial twisted modes by rapid parallel motions of electrons in a sheared magnetic geometry. The nonlinear coupling between the dominant unstable mode and its twisted modes is important for the saturation of KBM turbulence, in contrast to the importance of zonal flow shearing in ITG turbulence. The coupling depends on the flux-tube domain with the one-poloidal-turn parallel length and on the torus periodicity constraint.

Dynamics of the Chiral Phase Transition

The intention of this study is the search for signatures of the chiral phase transition in heavy-ion collisions. To investigate the impact of fluctuations, e.g., of the baryon number, at the transition or at a critical point, the linear sigma model is treated in a dynamical (3+1)-dimensional numerical simulation. Chiral fields are approximated as classical mean fields, and quarks are described as quasi particles in a Vlasov equation. Additional dynamics is implemented by quark-quark and quark-sigma-field interactions. For a consistent description of field-particle interactions, a new Monte-Carlo-Langevin-like formalism has been developed and is discussed.

Kinetic Ballooning Mode Turbulence Simulation based on Electromagnetic Gyrokinetics

The kinetic ballooning mode (KBM) turbulence in Tokamak plasma is investigated by electromagnetic gyrokinetic simulations. From the entropy balance analysis, it is revealed that the field-particle interactions transfer a significant fraction of the ion entropy produced by the instability to electrons. Then, the produced ion entropy balances to the sum of the ion and electron dissipations at the saturation of the KBM instability growth, in contrast to ITG turbulence where ion entropy production mostly balances to ion dissipation.

Subwavelength particles in an inhomogeneous light field: optical forces associated with the spin and orbital energy flows

We analyse the ponderomotive action experienced by a small spherical particle immersed in an optical field, in relation to the internal energy flows (optical currents) and their spin and orbital constituents. The problem is studied analytically, on the basis of the dipole model, and numerically. The three sources of the field mechanical action—the energy density gradient and the orbital and spin parts of the energy flow—differ in their ponderomotive mechanisms, and their physical nature manifests itself in the dependence of the optical force on the particle radius a. If a ≪ λ (the radiation wavelength), the optical force behaves as aν, and integer ν can be used to classify the sources of the mechanical action. This classification correlates with the multipole representation of the field–particle interaction: the gradient force and the orbital momentum force appear due to the electric or magnetic dipole moments per se; the spin momentum force emerges due to interaction between the electric and magnetic dipoles or between the dipole and quadrupole moments (if the particle is polarizable electrically but not magnetically or vice versa). In principle, the spin and orbital currents can be measured separately through the probe particle motion, employing a special choice of particles with the necessary magnetic and/or electric properties.

GENERAL ECE THEORY OF FIELD AND PARTICLE INTERACTION: APPLICATION TO LOW ENERGY NUCLEAR REACTION (LENR)

The general ECE theory is developed of field interaction and particle interaction on the classical and quantum relativistic level using the minimal prescription. The theory conserves total energy (momentum and charge) current density, and is based on the development of the tetrad postulate of Cartan geometry into the EEC wave equation and fermion equation. The latter is developed for any kind of interaction between fields or between particles or particles and fields. In ECE theory all of these interactions are phenomena of spacetime represented by geometry. The general theory is applied to reproducible and repeatable experimental data from low energy nuclear reactions.

GENERAL ECE THEORY OF FIELD AND PARTICLE INTERACTION: APPLICATION TO LOW ENERGY NUCLEAR REACTION (LENR)

The general ECE theory is developed of field interaction and particle interaction on the classical and quantum relativistic level using the minimal prescription. The theory conserves total energy (momentum and charge) current density, and is based on the development of the tetrad postulate of Cartan geometry into the EEC wave equation and fermion equation. The latter is developed for any kind of interaction between fields or between particles or particles and fields. In ECE theory all of these interactions are phenomena of spacetime represented by geometry. The general theory is applied to reproducible and repeatable experimental data from low energy nuclear reactions.

Brownian Dynamics Simulations for Investigating Aggregate Structures in a Suspension Composed of Rod-Like Hematite Particles

We have investigated aggregation phenomena in a suspension composed of rod-like hematite particles, which have a magnetic moment normal to the particle axis direction, by means of Brownian dynamics simulations. The present Brownian dynamics method takes into account the spin rotational Brownian motion around the particle axis in addition to the ordinary translational and rotational Brownian motion. First, the validity of the present simulation method has been clarified by comparing with results obtained by the fully-established Monte Carlo method. Then, from performing the simulations, we have investigated the influences of magnetic particle-field and particle-particle interactions, shear rate and volumetric fraction of particles on particle aggregation phenomena. Snapshots of aggregate structures are used for qualitative discussion and cluster size distribution, radial distribution function and orientational correlation functions of the direction of particle axis and magnetic moment are focused on for quantitative discussion. The main results obtained here are summarized as follows. The raft-like clusters are significantly formed at a magnetic particle-particle interaction much larger than that for a magnetic spherical particle suspension. This is because the rotational Brownian motion has a significant influence on the formation of clusters for a suspension composed of rod-like particles with large aspect ratio. An applied magnetic field enhances the formation of raft-like clusters. A shear flow does not have a significant influence on the internal structures of clusters, but influences the cluster size distribution of raft-like clusters. The volumetric fraction of particles has a significant effect on the growth of raft-like clusters and clear cluster formation appears from a volumetric fraction between 0.01 and 0.05 in the present simulation circumstances.

Diffusion Coefficients, Short-Term Cosmic Ray Modulation, and Convected Magnetic Structures

Three cases of large-amplitude, small spatial-scale interplanetary particle gradients observed by the anticoincidence shield (ACS) aboard the INTEGRAL spacecraft in 2006 are investigated. The high data rates provided by the INTEGRAL ACS allow an unprecedented ability to probe the fine structure of GCR propagation in the inner Heliosphere. For two of the three cases, calculating perpendicular and parallel cosmic ray diffusion coefficients based on both field and particle data results in parallel diffusion appearing to satisfy a convection gradient current balance, provided that the magnetic scattering of the particles can be described by quasi-linear theory. In the third case, perpendicular diffusion seems to dominate. The likelihood of magnetic flux rope topologies within solar ejecta affecting the local modulation is considered, and its importance in understanding the field-particle interaction for the astrophysics of nonthermal particle phenomena is discussed.

On the Negative Magneto-Rheological Effect of a Suspension Composed of Rod-Like Hematite Particles by Means of Brownian Dynamics Simulations with Spin Brownian Motion

We have investigated the behaviors of rod-like hematite particles in a simple shear flow as well as in an applied magnetic field, in order to clarify the dependence of the negative magneto-rheological effect on particle aggregation and orientational distribution of particles. The present Brownian dynamics method has a significant advantage that it takes into account the spin rotational Brownian motion around the particle axis in addition to the ordinary translational and rotational Brownian motion. The net viscosity is decomposed into three components and discussed at a deeper level and in more detail: these three viscosity components arise from (a) the torque due to the magnetic particle-field interaction and (b) the torque and (c) the force due to the interaction between particles. In contrast to the ferromagnetic rod-like particle that exhibits a single-peak-type orientational distribution, the present hematite particle has a linear-peak-type distribution with a much more gentle profile. Hence, the orientational distribution does not change significantly. However, this slightly reformed distribution makes a significant influence on the negative magneto-rheological effect. In a dilute suspension, the effect of the magnetic field strength on this negative magneto-rheological effect is qualitatively and quantitatively in good agreement with that obtained by the previous theory and Brownian dynamics simulations without translational Brownian motion. In a relatively dense suspension, the viscosity components arising from an applied magnetic field and the interaction between particles come to change rapidly since certain strength of magnetic particle-particle interaction, which is due to the formation of raft-like clusters.

The invariant representation of generalized momentum

The relativistic-invariance representation of generalized momentum of a particle in the external field is proposed. In this representation the dependence of potentials of the particle-field interaction on the particle velocity is taken into account. An exact correspondence of expressions for the energy and potential energy for the classical Hamiltonian is established, which makes identical the solutions of problems of mechanics with relativistic and classical approaches. The invariance of the generalized momentum representation allows one to describe equivalently a physical system in geometrically conjugated spaces of kinematical and dynamical variables.

Scattering of inhomogeneous circularly polarized optical field and mechanical manifestation of the internal energy flows

Based on the Mie theory and on the incident beam model via superposition of two plane waves, we analyze numerically the momentum flux of the field scattered by a spherical, nonmagnetic microparticle placed within the spatially inhomogeneous circularly polarized paraxial light beam. The asymmetry between the forward- and backward-scattered momentum fluxes in the Rayleigh scattering regime appears due to the spin part of the internal energy flow in the incident beam. The transverse ponderomotive forces exerted on dielectric and conducting particles of different sizes are calculated and special features of the mechanical actions produced by the spin and orbital parts of the internal energy flow are recognized. In particular, the transverse orbital flow exerts the transverse force that grows as ${a}^{3}$ for conducting and as ${a}^{6}$ for dielectric subwavelength particle with radius $a$, in compliance with the dipole mechanism of the field-particle interaction; the force associated with the spin flow behaves as ${a}^{8}$ in both cases, which testifies for the nondipole mechanism. The results can be used for experimental identification and separate investigation of the spin and orbital parts of the internal energy flow in light fields.

Three-Dimensional Numerical Simulation of a 30-GHz Gyrotron Resonator With an Explicit High-Order Discontinuous-Galerkin-Based Parallel Particle-In-Cell Method

Fast design codes for the simulation of the particle–field interaction in the interior of gyrotron resonators are available. They procure their rapidity by making strong physical simplifications and approximations, which are not known to be valid for many variations of the geometry and the operating setup. For the first time, we apply a fully electromagnetic (EM) transient 3-D high-order discontinuous Galerkin particle-in-cell method solving the complete self-consistent nonlinear Vlasov–Maxwell equations to simulate a 30-GHz high-power millimeter-wave gyrotron resonator without physical reductions. This is a computational expensive endeavor, which requires today's high-performance computing capacity. However, this enables a detailed analysis of the EM field, the excited <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\hbox{TE}_{2, 3}$</tex></formula> mode, the frequencies, and the azimuthal particle bunching in the beam. Therefrom, we present new insights into the complex particle–field interaction of the electron cyclotron maser instability transferring kinetic energy from the electron beam to the EM field.

Mechanical Action of Inhomogeneously Polarized Optical Fields and Detection of the Internal Energy Flows

We analyze numerically correspondence between the mechanical action, experienced by a spherical microparticle, and the internal energy flows in the light field incident on the particle. The inhomogeneous incident field is modelled by superposition of two plane waves; the mechanical action is calculated via the Mie theory for dielectric and conducting particles of different sizes and optical properties. It is shown that both spin and orbital components of the field momentum can produce the mechanical action whose value and sign depend on many additional details of the field-particle interaction. Besides, forces that are not associated with any sort of the energy flow (e.g., the gradient force owing to the inhomogeneous intensity and the polarization-dependent dipole force emerging due to inhomogeneous polarization) can strongly modify the observed mechanical action. The polarization-dependent mechanical action on particles can be treated as a form of the spin-orbit interaction of light.

Simulations of self-organization of bubbles in acoustic fields in three dimensions

Self-organization of bubbles (structure formation) and related self-action of the acoustic field is a strongly non-linear phenomenon, which is observed, e.g., in acoustic cavitation and sonochemical reactors. The phenomenon is a manifestation of a two-way field-particle interaction, when the bubbles change their position and sizes due to the Bjerknes and other forces and rectified diffusion, and affect the acoustic properties of the medium, which leads to restructuring of the acoustic field. The models of this phenomenon available in literature are revised, and a model based on the spatio-temporal averaging, which includes the above mentioned effects, is derived. Based on this model, a 3-D pseudospectral code for simulation of bubble self-organization is developed and tested. Simulations show interesting spatio-temporal behavior of the bubbles and the acoustic field, which is initialized as a standing wave but may drastically change its structure due to bubble dynamics (especially near the resonance). Bubble pattern formation is sensitive to many parameters including parameters of the acoustic field, bubble initial size, number density, spatial distribution, and ambient conditions. The effects found in the result of simulations are discussed. [This research is supported by the Grant of the Ministry of Education and Science of the Russian Federation (G34.31.0040).]

Analysis of Assembling ZnO Nanoparticles Into Nanogap Electrodes for Nanoscale Electronic Device Applications

We report the assembly of semiconducting ZnO nanoparticles into nanogap electrodes using ac dielectrophoresis (DEP) process. ZnO nanoparticles were grown using sol-gel method. As grown ZnO nanoparticles (diameter approximately 4 nm) were in a quasi-crystalline state and with increase in annealing temperature (in air) upto 400 degrees C the crystallinity was found to increase as revealed by X-ray diffraction and transmission electron microscopy. Absorption spectroscopy revealed that absorption edge of the as grown and annealed samples exhibited a blue-shift and could be attributed to the size quantization. A strong band tailing in the absorption spectra indicates the presence of shallow defects in the nanoparticles. The annealed ZnO nanoparticles (diameter approximately 9 nm) were assembled into nanogap electrodes (60 nm) using DEP process. DEP parameters such as frequency, applied voltage, and time were optimized to assemble ZnO nanoparticles into nanogap electrodes. Frequency variation study revealed that positive DEP is active at frequencies less than 500 kHz, and the negative DEP starts dominating at 1 MHz. It was observed that when DEP force overcomes the Brownian motion, the nanoparticles start chaining together in the region between the electrodes tip due to particle-field and particle-particle interactions. Under the optimized DEP parameters such as frequency of 150 kHz, peak-to-peak voltage of 3 V, and trapping time of 30 s, a minimum number of ZnO nanoparticles were assembled into nanogap electrodes. The ZnO nanoparticles based device was studied for field effect transistor (FET) characteristics and the typical current-voltage (I(D)-V(DS)) characteristic curves as a function of gate voltage (V(G)) were obtained. The curves indicate that ZnO nanoparticles based FET exhibits a significant gate effect as the conductance of the ZnO nanoparticles increases with gate voltage suggesting n-type semiconducting behavior of ZnO nanoparticles. Results show the myriad potential of dielectrophoretically assembled ZnO nanoparticles into nanogap electrodes for designing nanoscale devices for electronic and optoelectronic applications.

Colloidal particles that make smart polymer composites deform and rotate

All particles experience forces and torques when subjected to electric and/or magnetic fields. Especially strong field-particle interactions characterize colloidal particles showing dielectric- and magnetic properties. In the presence of magnetic- and/or electric field, dielectrophoretic- and magnetophoretic forces and torques acting on particles result in locomotion and structure formation. If the particles are dispersed and stabilized in liquids the rheological behavior of these fluids (electrorheological- and magnetorheological fluids) is strong function of imposed field. If colloidal particles with special electric and magnetic properties are built into flexible polymer matrix, electric-, and magnetic field sensitive polymer gels and elastomers are obtained. The particles couple the shape of the gel (or elastomer) to the external fields. Shape distortion and locomotion occur instantaneously and disappears abruptly when electric- or magnetic field is applied or removed, respectively. This kind of change in the material properties can be applicable to a variety of fields as a new driving mechanism and can be exploited to construct new type of soft actuators sensors, micromachines, biomimetic energy transducing devices, controlled delivery systems as well as micromotors. In this paper a review of most important colloid electric- and magnetic phenomena for uncharged particles are presented.