3,539 research outputs found
Electric charge is a magnetic dipole when placed in a background magnetic field
It is demonstrated, owing to the nonlinearity of QED, that a static charge
placed in a strong magnetic field\ \ is a magnetic dipole (besides remaining
an electric monopole, as well). Its magnetic moment grows linearly with as
long as the latter remains smaller than the characteristic value of 1.2\cdot
10^{13}\unit{G} but tends to a constant as exceeds that value. The force
acting on a densely charged object by the dipole magnetic field of a neutron
star is estimated
Magnetic response to applied electrostatic field in external magnetic field
We show, within QED and other possible nonlinear theories, that a static
charge localized in a finite domain of space becomes a magnetic dipole, if it
is placed in an external (constant and homogeneous) magnetic field in the
vacuum. The magnetic moment is quadratic in the charge, depends on its size and
is parallel to the external field, provided the charge distribution is at least
cylindrically symmetric. This magneto-electric effect is a nonlinear response
of the magnetized vacuum to an applied electrostatic field. Referring to a
simple example of a spherically-symmetric applied field, the nonlinearly
induced current and its magnetic field are found explicitly throughout the
space, the pattern of lines of force is depicted, both inside and outside the
charge, which resembles that of a standard solenoid of classical
magnetostatics
Magnetic response from constant backgrounds to Coulomb sources
Magnetically uncharged, magnetic linear response of the vacuum filled with
arbitrarily combined constant electric and magnetic fields to an imposed static
electric charge is found within general nonlinear electrodynamics. When the
electric charge is point-like and external fields are parallel, the response
found may be interpreted as a field of two point-like magnetic charges of
opposite polarity in one point. Coefficients characterizing the magnetic
response and induced currents are specialized to Quantum Electrodynamics, where
the nonlinearity is taken as that determined by the Heisenberg-Euler effective
Lagrangian.Comment: The part dealing with magnetically charged responses is removed to be
a subject of another paper after revisio
Noncommutative magnetic moment, fundamental length and lepton size
Upper bounds on fundamental length are discussed that follow from the fact
that a magnetic moment is inherent in a charged particle in noncommutative (NC)
electrodynamics. The strongest result thus obtained for the fundamental lenth
is still larger than the estimate of electron or muon size achieved following
the Brodsky-Drell and Dehlmet approach to lepton compositeness. This means that
NC electrodynamics cannot alone explain the whole existing descrepancy between
the theoretical and experimental values of the muon magnetic moment. On the
contrary, as measurements and calculations are further improved, the
fundamental length estimate based on electron data may go down to match its
compositeness radius
Pose consensus based on dual quaternion algebra with application to decentralized formation control of mobile manipulators
This paper presents a solution based on dual quaternion algebra to the
general problem of pose (i.e., position and orientation) consensus for systems
composed of multiple rigid-bodies. The dual quaternion algebra is used to model
the agents' poses and also in the distributed control laws, making the proposed
technique easily applicable to time-varying formation control of general
robotic systems. The proposed pose consensus protocol has guaranteed
convergence when the interaction among the agents is represented by directed
graphs with directed spanning trees, which is a more general result when
compared to the literature on formation control. In order to illustrate the
proposed pose consensus protocol and its extension to the problem of formation
control, we present a numerical simulation with a large number of free-flying
agents and also an application of cooperative manipulation by using real mobile
manipulators
New insights into electron spin dynamics in the presence of correlated noise
The changes of the spin depolarization length in zinc-blende semiconductors
when an external component of correlated noise is added to a static driving
electric field are analyzed for different values of field strength, noise
amplitude and correlation time. Electron dynamics is simulated by a Monte Carlo
procedure which keeps into account all the possible scattering phenomena of the
hot electrons in the medium and includes the evolution of spin polarization.
Spin depolarization is studied by examinating the decay of the initial spin
polarization of the conduction electrons through the D'yakonov-Perel process,
the only relevant relaxation mechanism in III-V crystals. Our results show
that, for electric field amplitude lower than the Gunn field, the dephasing
length shortens with the increasing of the noise intensity. Moreover, a
nonmonotonic behavior of spin depolarization length with the noise correlation
time is found, characterized by a maximum variation for values of noise
correlation time comparable with the dephasing time. Instead, in high field
conditions, we find that, critically depending on the noise correlation time,
external fluctuations can positively affect the relaxation length. The
influence of the inclusion of the electron-electron scattering mechanism is
also shown and discussed.Comment: Published on "Journal of Physics: Condensed Matter" as "Fast Track
Communications", 11 pages, 9 figure
Nigerian scam e-mails and the charms of capital
So-called '419' or 'advance-fee' e-mail frauds have proved remarkably successful. Global losses to these scams are believed to run to billions of dollars. Although it can be assumed that the promise of personal gain which these e-mails hold out is part of what motivates victims, there is more than greed at issue here. How is it that the seemingly incredible offers given in these unsolicited messages can find an audience willing to treat them as credible? The essay offers a speculative thesis in answer to this question. Firstly, it is argued, these scams are adept at exploiting common presuppositions in British and American culture regarding Africa and the relationships that are assumed to exist between their nations and those in the global south. Secondly, part of the appeal of these e-mails lies in the fact that they appear to reveal the processes by which wealth is created and distributed in the global economy. They thus speak to their readers’ attempts to map or conceptualise the otherwise inscrutable processes of that economy. In the conclusion the essay looks at the contradictions in the official state response to this phenomena
Noncommutative magnetic moment of charged particles
It has been argued, that in noncommutative field theories sizes of physical
objects cannot be taken smaller than an elementary length related to
noncommutativity parameters. By gauge-covariantly extending field equations of
noncommutative U(1)_*-theory to the presence of external sources, we find
electric and magnetic fields produces by an extended charge. We find that such
a charge, apart from being an ordinary electric monopole, is also a magnetic
dipole. By writing off the existing experimental clearance in the value of the
lepton magnetic moments for the present effect, we get the bound on
noncommutativity at the level of 10^4 TeV.Comment: 9 pages, revtex; v2: replaced to match the published versio
- …