Dipole Moments Of Particles Research Articles

Mode-specific directional emission from hybridized particle-on-a-film plasmons

We investigate the electromagnetic interaction between a gold nanoparticle and a thin gold film on a glass substrate. The coupling between the particle plasmons and the surface plasmon polaritons of the film leads to the formation of two localized hybrid modes, one low-energy "film-like" plasmon and one high-energy plasmon dominated by the nanoparticle. We find that the two modes have completely different directional scattering patterns on the glass side of the film. The high-energy mode displays a characteristic dipole emission pattern while the low-energy mode sends out a substantial part of its radiation in directions parallel to the particle dipole moment. The relative strength of the two radiation patterns vary strongly with the distance between the particle and the film, as determined by the degree of particle-film hybridization.

Searching for the electron EDM in a storage ring

Searches for permanent electric dipole moments (EDM) of fundamental particles have been underway for more than 50 years with null results. Still, such searches are of great interest because EDMs arise from radiative corrections involving processes that violate parity and time-reversal symmetries, and through the CPT theorem, are sensitive to CP-violation. New models of physics beyond the standard model predict new sources of CP-violation leading to dramatically enhanced EDMs possibly within the reach of a new generation of experiments. We describe a new approach to electron EDM searches using molecular ions stored in a tabletop electrostatic storage ring. Molecular ions with long-lived paramagnetic states such as tungsten nitride WN+ can be injected and stored in larger numbers and with longer coherence times than competing experiments, leading to high sensitivity to an electron EDM. Systematic effects mimicking an EDM such as those due to motional magnetic fields and geometric phases are found not to limit the approach in the short term, and sensitivities of δ|de| ≈ 10−30 e·cm/day appear possible under conservative conditions.

Yttrium barium copper oxide-filled polystyrene as a dielectric material

Electrical impedance measurements are car- ried out on high temperature superconducting ceramic Yt- trium Barium Copper Oxide (YBCO)-Polystyrene (PS) composite materials, in which superconducting particles are embedded in polystyrene matrix. The results of imped- ance versus frequency (100 Hz-13 MHz), phase angle versus temperature for volume percentage of supercon- ductor (0-40%) are presented. No marked transition in phase angle is observed when the material goes through the superconducting transition temperature of the filler. The dielectric constant and losses increase with increas- ing YBCO content. However the increase in losses is modest and the excellent dielectric properties of the composites are not adversely affected. The system con- forms to Clausius-Mossotti equation. Dipole moment of YBCO particles and polarizability of the composites are calculated using the Clausius-Mossotti approaches. V C 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120: 2233- 2241, 2011

Topological Phases of Dipolar Particles in Elongated Wannier Orbitals

We show that topological phases with fractional excitations can occur in two-dimensional ultracold dipolar gases on a particular class of optical lattices. Because of the dipolar interaction and lattice confinement, a quantum dimer model emerges naturally as the effective theory describing the low-energy behaviors of these systems under well-controlled approximations. The desired hierarchy of interaction energy scales is achieved by controlling the anisotropy of the orbital dimers and the dipole moments of particles. Experimental realization and detection of various phases are discussed, as well as the possible relevance for quantum computation.

Polarization of Nanorods Submerged in an Electrolyte Solution and Subjected to an ac Electrical Field

Recently, there has been growing interest in utilizing electrical fields to position and separate rod-shaped particles such as DNA molecules, actin filaments, microtubules, viruses, bacteria, nanotubes, and nanorods. The polarization of the electrical double layer, enveloping the rod, plays a critical role in determining the magnitude and direction of the rod's dipole moment. We consider noninteracting, rod-shaped (spherocylinder) particles and calculate the induced dipole moment as a function of the electrical field frequency, the rod's aspect ratio (length/radius), the rod's free surface charge, and the double-layer thickness. To this end, we solve the Poisson-Nernst-Planck (PNP) equations for the ions' migration, diffusion, and convection. When the surface charge is small and the rod is short, the dipole moment is negative. As the rod's length increases, the dipole moment increases and eventually changes sign from negative to positive. The dipole coefficient of a rod, whose length is greater than some critical value, increases linearly with length. This latter observation simplifies the estimation of the dipole moment of particles with large aspect ratios (length/radius). The theoretical predictions are compared and favorably agree with experimental data for double-stranded, short DNA molecules.

Magnetic moment generation from non-minimal couplings in a scenario with Lorentz-symmetry violation

This paper deals with situations that illustrate how the violation of Lorentz symmetry in the gauge sector may contribute to magnetic moment generation of massive neutral particles with spin- $\frac {1}{2}$ and spin-1. The procedure we adopt here is based on Relativistic Quantum Mechanics. We work out the non-relativistic regime that follows from the wave equation corresponding to a certain particle coupled to an external electromagnetic field and a background that accounts for the Lorentz-symmetry violation, and we thereby read off the magnetic dipole moment operator for the particle under consideration. We keep track of the parameters that govern the non-minimal electromagnetic coupling and the breaking of Lorentz symmetry in the expressions we get for the magnetic moments in the different cases we contemplate. Our claim is that the tiny magnetic dipole moment of truly-elementary neutral particles might signal Lorentz-symmetry violation.

Electric dipole moments as probes ofCPTinvariance

Electric dipole moments (EDMs) of elementary particles and atoms probe violations of $T$ and $P$ symmetries and consequently of $CP$ if $CPT$ is an exact symmetry. We point out that EDMs can also serve as sensitive probes of $CPT$-odd, $CP$-even interactions, that are not constrained by any other existing experiments. Analyzing models with spontaneously broken Lorentz invariance, we calculate EDMs in terms of the leading $CPT$-odd operators to show that experimental sensitivity probes the scale of $CPT$ breaking as high as ${10}^{12}\text{ }\text{ }\mathrm{GeV}$.

Landau analog levels for dipoles in non-commutative space and phase space

We investigate the analog of Landau quantization, for a neutral polarized particle in the presence of homogeneous electric and magnetic external fields, in the context of non-commutative quantum mechanics. This particle, possessing electric and magnetic dipole moments, interacts with the fields via the Aharonov–Casher and He–McKellar–Wilkens effects. For this model we obtain the Landau energy spectrum and the radial eigenfunctions of the non-commutative space coordinates and non-commutative phase space coordinates. Also we show that the case of non-commutative phase space can be treated as a special case of the usual non-commutative space coordinates.

Moment distributions of clusters and molecules in the adiabatic rotor model

We present a Fortran program to compute the distribution of dipole moments of free particles for use in analyzing molecular beams experiments that measure moments by deflection in an inhomogeneous field. The theory is the same for magnetic and electric dipole moments, and is based on a thermal ensemble of classical particles that are free to rotate and that have moment vectors aligned along a principal axis of rotation. The theory has two parameters, the ratio of the magnetic (or electric) dipole energy to the thermal energy, and the ratio of moments of inertia of the rotor. Program summary Program title:AdiabaticRotor Catalogue identifier:ADZO_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/ADZO_v1_0.html Program obtainable from:CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions:Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.:479 No. of bytes in distributed program, including test data, etc.:4853 Distribution format:tar.gz Programming language:Fortran 90 Computer:Pentium-IV, Macintosh Power PC G4 Operating system:Linux, Mac OS X RAM:600 Kbytes Word size:64 bits Classification:2.3 Nature of problem:The system considered is a thermal ensemble of rotors having a magnetic or electric moment aligned along one of the principal axes. The ensemble is placed in an external field which is turned on adiabatically. The problem is to find the distribution of moments in the presence of the external field. Solution method:There are three adiabatic invariants. The only nontrivial one is the action associated with the polar angle of the rotor axis with respect to external field. It is found by Newton's method. Running time:3 min on a 3 GHz Pentium IV processor.

Dipolar structures in magnetite ferrofluids studied with small-angle neutron scattering with and without applied magnetic field

Field-induced structure formation in a ferrofluid with well-defined magnetite nanoparticles with a permanent magnetic dipole moment was studied with small-angle neutron scattering (SANS) as a function of the magnetic interactions. The interactions were tuned by adjusting the size of the well-defined, single-magnetic-domain magnetite (Fe3O4) particles and by applying an external magnetic field. For decreasing particle dipole moments, the data show a progressive distortion of the hexagonal symmetry, resulting from the formation of magnetic sheets. The SANS data show qualitative agreement with recent cryogenic transmission electron microscopy results obtained in 2D [Klokkenburg, Phys. Rev. Lett. 97, 185702 (2006)] on the same ferrofluids.

Baryogenesis and EDMs: Constraining CP Violation Beyond the Standard Model

New sources of CPviolation beyond the Standard Model may help the scenario of electroweak baryogenesis (EWB) to account for the baryon asymmetry of the universe, and may be detectable in searches for permanent electric dipole moments of fundamental particles. In this talk, I focus on the calculation of the sources and relaxation rates in the transport equations for particle densities in the closed time path formalism of quantum field theory, suitable for the finite temperature and out-of-equilbrium conditions present at the electroweak phase transition. Applying the methods of closed time-path quantum field theory to derive transport equations relevant for EWB in the MSSM, we find regions of the parameter space where generation of the baryon asymmetry is resonantly enhanced, allowing successful baryogenesis with CP-violating phases small enough to be consistent with experimental limits on electron and neutron EDMs

Equation of spin motion in storage rings in the cylindrical coordinate system

The exact equation of spin motion in a cylindrical coordinate system with allowance for electric dipole moments of particles has been derived. This equation is convenient for analytical calculations of spin dynamics in circular storage rings when the configuration of main fields is simple enough. The generalized formula for the influence of a vertical betatron oscillation on the angular velocity of spin rotation has been found. This formula agrees with the previously obtained result and contains an additional oscillatory term that can be used for fitting. The relative importance of terms in the equation of spin motion is discussed.

New method of measuring electric dipole moments in storage rings.

A new highly sensitive method of looking for electric dipole moments of charged particles in storage rings is described. The major systematic errors inherent in the method are addressed and ways to minimize them are suggested. It seems possible to measure the muon EDM to levels that test speculative theories beyond the standard model.

Collective contributions to the dielectric relaxation of hydrogen-bonded liquids.

Dielectric relaxation times are often interpreted in terms of the reorientation of dipolar species or aggregates. The relevant time correlation function contains, however, cross terms between dipole moments of different particles. In the static case, these cross terms are accounted for by the Kirkwood factor g(K). Theories and molecular dynamics simulations suggest that such cross correlations may also affect the time-dependent properties, as reflected in the dielectric spectra. We present an experimental method for detecting effects of such cross correlations in dielectric spectra by a comparative analysis of dielectric and magnetic relaxation data. We demonstrate that such collective contributions can substantially affect dielectric relaxation. Experiments for n-pentanol (g(K)=3.06 at 298 K) and 2,2-dimethyl-3-ethyl-pentane-3-ol (g(K)=0.59) and their solutions in carbon tetrachloride show that in systems with g(K)>1, the cross correlations slow down dielectric relaxation. In systems with g(K)<1, dielectric relaxation is enhanced. The results conform to theoretical predictions by Madden and Kivelson [Adv. Chem. Phys. 56, 467 (1984)] and to results of molecular dynamics simulations. The relaxation enhancement by cross terms in the case of g(K)<1 is difficult to rationalize by conventional models of dielectric relaxation.

Critical role of flow-modified permittivity in electrorheology: model and computer simulation.

We propose a model that takes into account the effect of flow-modified permittivity (FMP) on electrorheology (ER). Our computer simulation shows that for Mason numbers less than 0.1, ER effects are mainly attributable to the deformation of chain structures, in agreement with earlier theoretical and simulation work. At larger Mason numbers, where chain structures have been destroyed by shear flows, we show that an FMP-induced misalignment between the particle dipole moments and the applied electric field plays a crucial role in producing ER effects. We also identify conditions under which negative ER effects are seen at large Mason numbers.

Fundamental Symmetries and Atomic Physics

A general introduction, on an intuitive level, is presented to discrete symmetries of physical laws: P, C, T and CPT. The accurate measurement of the weak nuclear charge in atomic cesium serves as a precision test of the Standard Model. The discovery of the nuclear anapole moment, a new P odd electromagnetic multipole, in the cesium experiment gives a first-rate information on parity-nonconserving nuclear forces. New prospects in the field are discussed. Upper limits on the dipole moments of elementary particles and atoms are presented, and their physical implications discussed. The atomic experiments are demonstrated to be as informative in this respect as the neutron ones. Tremendous progress in the field can be expected from experiments at ion storage rings and linear electrostatic traps.

Molecular dynamics study on the equilibrium magnetization properties and structure of ferrofluids.

We investigate in detail the initial susceptibility, magnetization curves, and microstructure of ferrofluids in various concentration and particle dipole moment ranges by means of molecular dynamics simulations. We use the Ewald summation for the long-range dipolar interactions, take explicitly into account the translational and rotational degrees of freedom, coupled to a Langevin thermostat. When the dipolar interaction energy is comparable with the thermal energy, the simulation results on the magnetization properties agree with the theoretical predictions very well. For stronger dipolar couplings, however, we find systematic deviations from the theoretical curves. We analyze in detail the observed microstructure of the fluids under different conditions. The formation of clusters is found to enhance the magnetization at weak fields and thus leads to a larger initial susceptibility. The influence of the particle aggregation is isolated by studying ferro-solids, which consist of magnetic dipoles frozen in at random locations but which are free to rotate. Due to the artificial suppression of clusters in ferrosolids the observed susceptibility is considerably lowered when compared to ferrofluids.

THE SIGNIFICANCE OF FLOW-MODIFIED PERMITTIVITY: A NEW MODEL AND COMPUTER SIMULATION OF ELECTRORHEOLOGY

We propose a model that takes into account the effect of flow-modified permittivity on electrorheology (ER). Due to dielectric relaxation, a shear flow causes the induced particle dipole moments in an ER fluid to tilt in a direction away from the direction of the applied DC electric field. Results from our computer simulation indicate that at high shear rates this misalignment (tilt angle) between the particle dipole moments and the applied electric field plays a crucial role in producing ER effects. By choosing particle-fluid dielectric and conductive mismatches to optimize the tilt angle, our simulation produces ER effects at much higher shear rates than those in earlier simulation work, even though there is no chain structure at these high shear rates. The increase in shear stress due to the applied electric field in our simulation is nearly constant over the wide range of shear rates examined, in qualitative agreement with experimental results. In addition, our model generates results that agree with earlier simulation work at low shear rates, where the particle dipole moments are essetially aligned with the field and the chain model is adequate.

Nonequilibrium Brownian dynamics analysis of negative viscosity induced in a magnetic fluid subjected to both ac magnetic and shear flow fields.

We study the rheological and magnetic characteristics of a magnetic fluid. The system, which we investigate, is as follows. Ferromagnetic particles are dispersed in a solvent, which is subjected to both ac magnetic and shear flow fields. The translational and rotational motions of particles are calculated by the Brownian dynamics method based on Langevin equations and the rheological and magnetic characteristics of the magnetic fluid system are estimated. First, we investigate the rheological and magnetic characteristics of the system in a dc magnetic field and then we analyze the effect of an ac magnetic field on those characteristics. We find that the negative viscosity effect is induced at a certain frequency range of the ac magnetic field. We also find that there are two main mechanisms responsible for the occurrence of negative viscosity. (1) Resonance between the rotational motions of the dipoles of particles and the fluctuation of ac magnetic fields occurs when applied magnetic fields are weak compared to the shear rate, in which case particles can still rotate in magnetic fields. Beyond this resonance frequency, negative viscosity appears. (2) The magnetic dipole moments of particles are forced to stay in the direction of the magnetic field when strong magnetic fields are applied in relatively low shear flow fields. However, negative viscosity occurs when the frequency of external magnetic fields exceeds a critical value, in which case the dipoles rotate continuously in a shear flow without stopping. In both cases, the mean angular velocity of the particles becomes higher than that of the solvent.

Cross terms and Kirkwood factors in dielectric relaxation of pure liquids

Dielectric relaxation reflects fluctuations of the total electric dipole moment of a liquid sample. If summed over molecular dipole moments, one obtains cross terms between molecular dipole moments of different particles which reflect collective contributions to dielectric relaxation. In the static case these collective effects are characterized by the well-known Kirkwood correlation factor g K . By comparing the dielectric relaxation times τ d of pure liquids with the single particle relaxation times τ s estimated from nuclear magnetic relaxation data, we show that collective effects affect the dynamical dielectric behavior. There is evidence for a relation of the simple form τ d = g K τ s .