Application of the dissipative particle dynamics method to magnetic colloidal dispersions

The validity of the application of the dissipative particle dynamics (DPD) method to ferromagnetic colloidal dispersions has been investigated by conducting DPD simulations for a two–dimensional system. First, the interaction between dissipative and magnetic particles has been idealized as some model potentials, and DPD simulations have been carried out using such model potentials for a two magnetic particle system. In these simulations, attention has been focused on the collision time for the two particles approaching each other and touching from an initially separated position, and such collision time has been evaluated for various cases of mass and diameter of dissipative particles and model parameters, which are included in defining the equation of motion of dissipative particles. Next, a multi–particle system of magnetic particles has been treated, and particle aggregates have been evaluated, together with the pair correlation function along an applied magnetic field direction. Such characteristics of aggregate structures have been compared with the results of Monte Carlo and Brownian dynamics simulations in order to clarify the validity of the application of the DPD method to particle dispersion systems. The present simulation results have clearly shown that DPD simulations with the model interaction potential presented here give rise to physically reasonable aggregate structures under circumstances of strong magnetic particle–particle interactions as well as a strong external magnetic field, since these aggregate structures are in good agreement with those of Monte Carlo and Brownian dynamics simulations.     

Scattering and absorption of particles by a black hole involving a global monopole

Under the conditions that the wavelength of a particle is much larger than its radius of central mass, and the Schwarzschild field is weak, the scattering of a particle has been studied by many researchers. They obtained that scalar and vector particles abide by Rutherford’s angle distribution by using the low level perturbation method and the scattered field’s approximation in a weak field. The scattering cross section of a photon coincides with the section in Newton’s field of point mass. We can obtain the photon’s polarization effect by calculating the second-order perturbation in the linear Schwarzschild field. This article discusses the scattering and absorption of a particle by a black hole involving a global monopole by using the aforesaid method.     

正交电磁场中粒子束的质量聚焦及粒子轨迹

<正>交电磁场中粒子的运动轨迹在拐点处按指数规律变化,使不同质量离子的轨迹有明显区别,由此可创建新的电磁核素分离法。从牛顿运动方程出发,基于单粒子轨道法阐述被分离核素在正交电磁场中的运动规律,重点找出轨迹的拐点。给出了多质量粒子束在正交电磁场中的质量聚焦特性,以Li离子为例,应用MATLAB模拟粒子束的运动轨迹,结果表明正交电磁场中可实现多质量束流的质量分离。总结出粒子轨迹方程的特点,为多质量束流分离结构的工程化实现提供参数。研究成果可应用到质量分离器、质谱分析仪及材料提纯等装置的研制中,同时对于特殊位形电磁场控制多质量束流等相关领域的研究亦有一定的参考价值。     

Probing the Higgs field using massive particles as sources and detectors

In the standard model, all massive elementary particles acquire their masses by coupling to a background Higgs field with a non-zero vacuum expectation value. What is often overlooked is that each massive particle is also a source of the Higgs field. A given particle can in principle shift the mass of a neighboring particle. The mass shift effect goes beyond the usual perturbative Feynman diagram calculations which implicitly assume that the mass of each particle is rigidly fixed. Local mass shifts offer a unique handle on Higgs physics since they do not require the production of on-shell Higgs bosons. We provide theoretical estimates showing that the mass shift effect can be large and measurable, especially near pair threshold, at both the Tevatron and the LHC. PACS 14.80.Bn; 13.40.Dk     

On the existence of zero rest mass particles

It is shown that no concrete particle can have zero rest mass. A separate photon is proven to be a concrete particle. The nonexistence of the electromagnetic field as an independent physical reality is demonstrated. The existence of a subatomic electromagnetic particle of a very small rest mass, theemon, instead of the electromagnetic field, is stated. The compatibility of the notion of the emon with the special relativity theory is elucidated. Some corollaries of the existence of the emon as well as the possibilities of determining its rest mass are discussed. The explanations of the relativity aberration and Doppler effect in terms of the emon are given. The importance of the principle of concreteness of experiments is emphasized and illustrated. Some related problems are noticed.     

Equivalence of Two Definitions of the Effective Mass of a Polaron

Two definitions of the effective mass of a particle interacting with a quantum field, such as a polaron, are considered and shown to be equal in models similar to the Fröhlich polaron model. These are: 1. the mass defined by the low momentum energy E(P)≈E(0)+P ²/2M of the translation invariant system constrained to have momentum P and 2. the mass M of a simple particle in an arbitrary slowly varying external potential, V, described by the nonrelativistic Schrödinger equation, whose ground state energy equals that of the combined particle/field system in a bound state in the same V.     

Theories of Variable Mass Particles and Low Energy Nuclear Phenomena

Variable particle masses have sometimes been invoked to explain observed anomalies in low energy nuclear reactions (LENR). Such behavior has never been observed directly, and is not considered possible in theoretical nuclear physics. Nevertheless, there are covariant off-mass-shell theories of relativistic particle dynamics, based on works by Fock, Stueckelberg, Feynman, Greenberger, Horwitz, and others. We review some of these and we also consider virtual particles that arise in conventional Feynman diagrams in relativistic field theories. Effective Lagrangian models incorporating variable mass particle theories might be useful in describing anomalous nuclear reactions by combining mass shifts together with resonant tunneling and other effects. A detailed model for resonant fusion in a deuterium molecule with off-shell deuterons and electrons is presented as an example. Experimental means of observing such off-shell behavior directly, if it exists, is proposed and described. Brief explanations for elemental transmutation and formation of micro-craters are also given, and an alternative mechanism for the mass shift in the Widom–Larsen theory is presented. If variable mass theories were to find experimental support from LENR, then they would undoubtedly have important implications for the foundations of quantum mechanics, and practical applications may arise.     

Negative viscosity due to magnetic properties of a non-dilute suspension composed of ferromagnetic rod-like particles with magnetic moment normal to the particle axis

The negative viscosity of a colloidal dispersion composed of ferromagnetic rod-like particles, which have a magnetic moment normal to the particle axis, have been investigated. A simple shear flow problem has been treated to clarify the particle orientational distribution and rheological properties of such a semi-dense dispersion, under circumstances of an external magnetic field applied in the direction normal to the shear plane of a simple shear flow. The results obtained here are summarized as follows. For the cases of a very strong magnetic field and magnetic interactions between particles, the magnetic moment of the rod-like particles is significantly restricted in the magnetic field direction, so that the particle approximately aligns in the shear flow direction. Also, the particle can easily rotate around the axis of the cluster almost freely even in a simple shear flow. Characteristic orientational properties of the particle cause negative viscosity, as in the previous study for a dilute dispersion. However, magnetic particle-particle interactions have a function to make such negative viscosity decrease.     

On the orientational characteristics and transport coefficients of an oblate spheroidal hematite particle in a simple shear flow

We have developed the basic equation of the orientational distribution function of oblate spheroidal hematite particles with rotational Brownian motion in a simple shear flow under an applied magnetic field. An oblate spheroidal hematite particle has an important characteristic in that it is magnetized in a direction normal to the particle axis. Since a dilute dispersion is addressed in the present study, we have taken into account only the friction force (torque) whilst neglecting the hydrodynamic interactions among the particles. This basic equation has been solved numerically in order that we may investigate the dependence of the orientational distribution on the magnetic field strength, shear rate and rotational Brownian motion and the relationship between the orientational distribution and the transport coefficients such as viscosity and diffusion coefficient. We found that if the effect of the magnetic field is more dominant, the particle inclines in such a way that the oblate surface aligns in the magnetic field direction. If the Peclet number increases and the effect of the shear flow becomes more dominant, the particle inclines such that the oblate surface tilts in the shear flow direction. The viscosity due to the magnetic torque is shown to increase as the magnetic field increases, since the magnetic torque due to the applied magnetic field becomes the more dominant effect. Moreover, the viscosity increase is shown to be more significant for a larger aspect ratio or for a more oblate hematite particle. We have applied the analysis to the problem of particle sedimentation under gravity in the presence of a magnetic field applied in the sedimentation direction. The particles are found to sediment with the oblate surface aligning more significantly in the sedimentation direction as the applied magnetic field strength increases.     

Technical Improvements in the Experiment of Isochronous Mass Measurement of 58Ni Projectile Fragments

 The combination of in-flight fragment separator and the isochronous mass spectrometry(IMS) in storage rings have been proven to be a powerful tool for the precision mass measurements of shortlived exotic nuclei. In IMS, the mass-over-charge ratio is only related to the revolution period of stored ions, and the relative mass resolution can reach up to the order of 10−6. However, the instability of the magnetic field of storage ring deteriorates the resolution of revolution period, making it very difficult to distinguish the ions with very close mass-over-charge ratio via their revolution periods. To improve the resolution of revolution periods, a new method of weighted shift correction (WSC) has been developed to accurately correct the influence of the magnetic field instabilities in the isochronous mass measurements of 58Ni projectile fragments. By using the new method, the influence of unstable magnetic fields can be greatly reduced, and the mass resolution can be improved by a factor up to 1.7. Moreover, for the ions that still cannot be distinguished after correcting the magnetic field instabilities, we developed a new method of pulse height analysis for particle identification. By analyzing the mean pulse amplitude of each ion from the timing detector, the stored ions with close mass-over-charge ratios but different charge states such as 34Ar and 51Co can be identified, and thus the mass of 51Co can be determined. The charge-resolved IMS may be helpful in the future experiments of isochronous mass measurement even for N =Z nuclei.     

Quasi-2D Monte Carlo simulations of a colloidal dispersion composed of magnetic plate-like particles with magnetic moment normal to the particle axis

We have investigated aggregation phenomena of a colloidal dispersion composed of magnetic plate-like particles by means of Monte Carlo simulations. Such plate-like particles have been modelled as disk-like particles with magnetic moment normal to the particle axis at the particle centre, with the section shape of a spherocylinder. The main objective of the present study is to clarify the influences of the magnetic field strength and magnetic interactions between particles on particle aggregation phenomena. We have concentrated our attention on a quasi-2D system from an application point of view such as the development of surface quality changing technology using such magnetic plate-like particles. A magnetic field is applied along the direction perpendicular to the plane of the monolayer. Internal structures of particle aggregates are discussed quantitatively in terms of radial distribution and orientational pair correlation functions. For the case of strong magnetic interactions between particles, particles form long column-like clusters with their magnetic moments alternating in direction between the neighbouring particles. These tendencies appear under circumstances of a weak applied magnetic field. However, as the magnetic field strength increases, particles incline towards the magnetic field direction, so that particles do not form such clusters.     

Regularization of the interaction and renormalization of the physical constants in the clothed particle representation within the quantum field theory

The possibility of covariant regularization of trilinear Yukawa-type interaction has been investigated within the simplified standard quantum field theory. The properties of the vertex functions, conditioned by the Lorentz invariance of particle mass shifts, and regularizing functions in the lowest interaction orders have been studied within the clothed-particle representation.     

Effect of Mass and Charge of Ionic Species on Spatio‐Temporal Evolution of Transient Electric Field in CCP Discharges

The formation of capacitive sheath and existence of the transition electric field between sheath edge and bulk plasma in RF‐CCP discharge is predicted (PRL 89, 265006 2002); such structures are sensitive to the plasma composition. On the basis of semi‐infinite particle‐in‐cell (PIC) simulation the effect of charge and mass of ionic species on the spatio‐temporal evolution of the transient electric field and phase mixing phenomena in linear and weakly nonlinear regime has been explored. As an important feature, the simulation results predict that the maximum amplitude of the transient electric field decreases with increasing ionic mass and charge; further the sheath width increases with increasing ionic mass while follow opposite trend with increasing ionic charge. The excitation of wave like structures in the transition region and efficient energy transport to the bulk region of CCP discharges in a nonlinear regime has also been predicted. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Motion of a Nonferromagnetic Particle in a Periodic Magnetic Field

The motion of a spherical nonferromagnetic particle in an axially symmetric periodic permanent magnetic field is considered. It is shown that in this field configuration the focusing of fast particles and the mass separation of a particle beam are realizable.     

On a generalization of the equations of electrodynamics

Both the field equations and the equations of motion of a charged particle in an electromagnetic field are generalized. The sense of the generalization consists in giving up the Lorentz condition on the field potentials. The basic conclusion is that, in addition to the charge and mass, the proper rotation of the particle (the spin) should belong to the characteristics of a particle in classical electrodynamics.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 107–110, July, 1972.The author wishes to thank the participants of the Ivanov Inter-Institute Seminar on Mathematical and Theoretical Physics for discussion of the results of the present work.     

On the Charge Form Factor and Eigenvalue of Fermion Energy in a Three-Dimensional Electrodynamics

A static field and self-energy of a particle are considered for a particle charge distributed throughout a 2 + 1-measurement space. The potential of the static field for r has the same asymptotics as for the delta form factor, provided an account is taken of the contribution from vacuum polarization; at the origin of coordinates, the above potential is regular. The proposed form factor allows a relation for the particle charge distribution to be derived in a closed form. The diagonal tension-tensor components of the particle-generated field are found to vanish and the particle field mass calculated using the classical method appears to be finite in the case where the proposed form factor is used. This mass coincides with that obtained through quantum calculations by the order of magnitude.     

A different theory of anomalous magnetic moment

The invariance of Dirac's equation under rotation has been used to obtain the wave equation for a particle interacting with an electromagnetic field. The origin of the anomalous magnetic moment of a particle has been attributed to the existence of mass due to spin. These masses for a few representative particles have been calculated. In particular these calculations give a mass of 592.074 eV for a neutrino. An operator for the spin angular velocity has been constructed and the values of spin angular velocities for the particles have also been calculated.     

Speculations on quark observation

Results of non-perturbative calculations in several models of relativistic quantum field theory lead to the concept of a stable particle whose mass is not well defined. Assuming that quarks are such particles, we propose several possible methods of quark observation.     

Radiation Reaction of the Classical Off-Shell Relativistic Charged Particle

It has been shown by Gupta and Padmanabhan that the radiation reaction force of the Abraham–Lorentz–Dirac equation can be obtained by a coordinate transformation from the inertial frame of an accelerating charged particle to that of the laboratory. We show that the problem may be formulated in a flat space of five dimensions, with five corresponding gauge fields in the framework of the classical version of a fully gauge covariant form of the Stueckelberg–Feynman–Schwinger covariant mechanics (the zero mode fields of the 0, 1, 2, 3 components correspond to the Maxwell fields). Without additional constraints, the particles and fields are not confined to their mass shells. We show that in the mass-shell limit, the generalized Lorentz force obtained by means of the retarded Green's functions for the five dimensional field equations provides the classical Abraham–Lorentz–Dirac radiation reaction terms (with renormalized mass and charge). We also obtain general coupled equations for the orbit and the off-shell dynamical mass during the evolution as well as an autonomous non-linear equation of third order for the off-shell mass. The theory does not admit radiation if the particle does not move off-shell. The structure of the equations implies that mass-shell deviation is bounded when the external field is removed.     

Non-existence of the Reissner-Nordström repulsion in general relativity

The radial motion of a free neutral test particle in the Reissner-Nordström space-time is studied. It is shown that when the contribution of the electrical field energy to the mass of the central body is properly taken account of, there is no repulsion of the test particle inside the inner horizon of the space-time.