Residual resistivity dipoles

Current flow past lattice defects in metals is associated with a localized conduction band polarization. This has become generally recognized in electromigration theory, but there is disagreement about the details of the polarization pattern. Discussions by others have emphasized polarization terms which are first order in the perturbation potential. This paper analyzes the polarization terms which are proportional to scattering probabilities and thus related to the increase in resistivity. These are second order, or higher, in the scattering potential. A simple physical picture is used to estimate the size of this dipole moment associated with the residual resistivity. A quantum mechanical discussion is given for the one-dimensional case. The conditions under which the polarization can be expected to be linear in the scattering cross-section is discussed.     

Reconnecting coloured dipoles

Reconnections among the produced colour dipoles in the Dipole Cascade Model are discussed, and an implementation in theAriadne program is presented. The reconnections are shown to have only small effects on event shapes at LEP 1, on theW mass determination at LEP 2 and on rapidity gaps in deep inelastic scattering at HERA.     

Ionic dipoles in helium

Attention has been focused on the apparent indications of the existence of ionic dipoles in solid helium. The presence of identical quasiparticles in cryogenic liquids with a positive scattering length of embedded electrons has been suggested. Possible manifestations have been discussed, which would allow the detection of the gas of dipolar structures in superfluid helium and the investigation of its behavior.     

Dynamics of two interacting dipoles

We study the deterministic spin dynamic of two interacting magnetic moments with anisotropy and dipolar interaction under the presence of an applied magnetic field, by using the Landau–Lifshitz equation with and without a damping term. Due to different kinds of interactions, different time scales appear: a long time scale associated with the dipolar interaction and a short time scale associated with the Zeeman interaction. We found that the total magnetization is not conserved; furthermore, for the non-dissipative case it is a fluctuating function of time, with a strong dependence on the strength of the dipolar term. In the dissipative case there is a transient time before the total magnetization reaches its constant value. We examine this critical time as a function of the distance between the magnetic moments and the phenomenological damping coefficient, and found that it strongly depends on these control parameters.     

Dislocation dipoles of infinitesimal width

The stresses of a dislocation dipole of infinitesimal width are expressed by means of stress gradients of a dislocation. The long-range interaction of an edge dipole with a screw dislocation is discussed.The author is indebted to Professor J. J. Gilman for his interest and encouragement.     

The energy of dislocation dipoles

In conventional dislocation theory based on the concept of Volterra dislocations, the energy of coplanar dislocation dipoles cannot be obtained without introducing an ill-defined ad hoc annihilation distance. When the dislocations are described more realistically by Peierls dislocations, absolute values for the dipole energy can be obtained from physical arguments. It is found that when dislocations in a dipole come close, they may not annihilate each other but the dipole can collapse when the dislocations have reached a critical separation of several lattice constants.     

Rotating vortex dipoles in ferromagnets

Vortex-antivortex pairs are spontaneously created in magnetic elements. In the case of opposite vortex polarities the pair has a nonzero topological charge, and it behaves as a rotating vortex dipole. We find theoretically and confirm numerically its energy as a function of angular momentum and the associated rotation frequencies. The annihilation process of the pair changes the topological charge while the energy is monotonically decreasing. The change of topological charge affects the dynamics profoundly. We finally discuss the implications of our results for Bloch point dynamics.     

Residual resistivity dipoles in electromigration

In the presence of an electric field a driving force is exerted by the surrounding electron gas on the impurity atoms. The contribution from this term is usually referred to as the Bosvieux-Friedel term who related it to the residual resistivity of the impurity. It has been suggested that the residual resistivity of the impurity causes a dipolar buildup around the impurity resulting in the so-called residual resistivity dipoles (RRD's) which in turn contribute a term to the driving force, in addition to the Boxvieux-Friedel term. We discuss the nature of this term for an impurity in a jellium matrix using nonlinear screening theory. It is found to vanish if it is identified with the third order terms in the impurity potential representing contribution from the RRD's.     

Radiation of relativistic dipoles. I

In the proposed series of articles, a systematic exposition will be given of the classical theory of radiation of relativistic point dipoles. Specific examples of radiation having practical significance will also be considered. V. V. Kuibyshev Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 60–64, February, 1993.     

Magnetic particles with shifted dipoles

We present simulations and analytical calculations for a system of magnetic nano-particles that possess a dipole moment that is shifted out of the center of mass, towards the surface, leading to a further asymmetry of the dipolar interaction. In our contribution, we discuss the peculiarities of ground state small clusters, both, with and without an external magnetic field. Small clusters help us to get an insight into the inter-particle interactions and form a building block for studies of larger systems. Without external magnetic field, the ground state structure changes from chains and rings with parallel alignment of moments, usually observed in dipolar particles (Prokopieva et al., 2009 [1]), to pairs and triangles with close to anti-parallel orientation of moments, when the shift of the dipole is increased. We also present magnetization properties of larger systems at finite temperature and observe the influence of the shift in particular on the initial slope of the magnetization curve, namely, the initial susceptibility.     

Solvation forces in fluids

Using a formalism derived by us in an earlier paper we obtain the density profile and solvation force between two identical hard plates separated by a fluid characterized by (i) an Orstein-Zernike correlation function and (ii) a Percus-Yevick sticky sphere correlation function. Example (i) yields an exponential or hyperbolic density profile characterized by a correlation length ξ that diverges at the critical point as (T-T_c )^-v . The corresponding force is weak and attractive following an exponential law at large separations. Example (ii) yields an attractive force in the vicinity of the critical region and an oscillatory force at higher densities and/or higher temperatures which can significantly modify forces between colloid particles.     

Physical Modeling of Aqueous Solvation

We consider the free energies of solvating molecules in water. Computational modeling usually involves either detailed explicit-solvent simulations, or faster computations, which are based on implicit continuum approximations or additivity assumptions. These simpler approaches often miss microscopic physical details and non-additivities present in experimental data. We review explicit-solvent modeling that identifies the physical bases for the errors in the simpler approaches. One problem is that water molecules that are shared between two substituent groups often behave differently than waters around each substituent individually. One manifestation of non-additivities is that solvation free energies in water can depend not only on surface area or volume, but on other properties, such as the surface curvature. We also describe a new computational approach, called Semi-Explicit Assembly, that aims to repair these flaws and capture more of the physics of explicit water models, but with computational efficiencies approaching those of implicit-solvent models.     

Properties of spacetimes with magnetic dipoles

The properties of an asymptotically flat spacetime with a mass and a magnetic dipole are studied. We focus on the breaking of spherical symmetry by the magnetic dipole. We investigate the geometry of the spacetime through the trajectories of null geodesics and the embedding diagrams of various hypersurfaces, included constant t and r surfaces and the infinite red shift surface. We find that the effects of the magnetic dipole on the spacetime are larger at the poles than on the equator.     

Radiation by relativistic dipoles. II

In a continuation of an earlier study, the electromagnetic fields of a point magnetic moment — a magneton — in uniform rectilinear motion, with a given spin precession, are analyzed. It is shown that the same equations can be found through Lorentz transformations from the corresponding expressions in the rest frame. The relationship between the electric and magnetic fieldsE andH radiated by a point magnetic dipole moment and a point electric dipole moment is derived through the use of dual transformations of the electromagnetic field tensor. It is assumed that each moment is in relativistic and otherwise arbitrary motion. In the relativistic case, as in the nonrelativistic case, the switch is accompanied by the replacementsHE, E-H. A covariant formalism is developed for describing the electromagnetic fields in the wave zone. The electromagnetic field tensor associated with the radiation is analyzed.V. V. Kuibyshev Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 73–78, March, 1993.     

Universal three-body physics for fermionic dipoles

Our present study of the universal physics for three oriented fermionic dipoles in the hyperspherical adiabatic representation predicts a single long-lived three-dipole state, which exists in only one three-body symmetry and forms near a two-dipole resonance. Our analysis reveals the spatial configuration of the universal state and the scaling of its binding energy and lifetime with the strength of the dipolar interaction. In addition, three-body recombination of fermionic dipoles is found to be important even at ultracold energies. An additional finding is that an effective long-range repulsion arises between a dipole and a dipolar dimer that is tunable via dipolar interactions.     

Vortex dipoles in a viscous fluid

A stationary planar flow of an incompressible Stokes fluid with vertex dipoles in it is considered. Explicit formulas for one dipole and a periodic set of dipoles are obtained.     

Radiation by relativistic dipoles. V

A discussion is given of the correspondence principles in radiation by a point magnetic moment. It is shown that just as in the particular examples considered previously, the angular and spectral-angular distributions of the radiation, and its power in the classical and quantum radiation theory differ only by a coefficient of 1/4. It is established that this difference results from the fundamentally differing nature of the emission in the classical and quantum theories. In the quantum radiation theory the spin magnetic moment is explained by spin-flip transitions adapted to the direction conserving the spin, whereas in the classical theory this radiation is due to spin precession about the magnetic field.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 83–88, March, 1995.     

Radiation by relativistic dipoles. IV

An analysis is made of radiation emitted by a neutron moving in constant and homogeneous electromagnetic fields (EH whereE=H, andEH whereEH) as a supplement to the classical theory of radiation from a point magnetic moment (a magneton) developed by the authors. The results obtained are found to be in agreement with the radiation theory of Ternov, Bagrov, and others constructed on the basis of the Dirac-Pauli equation. A study is made of the spectral composition and the invariance properties of the total radiation power.Tomsk University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 63–71, February, 1995.     

Equilibrium and passing properties of dislocation dipoles

Static and dynamic properties of dislocation dipoles are investigated under isotropic and anisotropic elasticity. In elastically isotropic systems for a dislocation character between 35 and 40°, a dipole assumes the same stress-free equilibrium angle of 90° as the screw dipole. This can be affected by elastic anisotropy, as in Cu where the equilibrium angle assumed by a screw dipole (≈59°) is unchanged up to a dislocation character of 22°. In contrast, the static properties of near-edge dislocation dipoles are little influenced by elastic anisotropy. Certain dipole passing properties, not the passing stress however, are also modified by elastic anisotropy. For large heights and/or in the case of undissociated dislocations, the minimum passing stress corresponds to a dipole character of ～60° and it exhibits a sharp maximum in screw orientation. Reasonably moderate dislocation reorientations should facilitate the passing of near-screw dislocations in fatigue channels. Within a certain range of applied stresses, the passing of dipoles, comprised of unlike attractive dislocations, is accompanied by the sweeping of one dislocation by the other over a limited distance. Dissociation plays a prominent role in determining both static and dynamic properties for dipole heights less than a few times the dissociation distance of an isolated dislocation.