12,713 research outputs found
Spontaneous CPT Violation in Confined QED
Symmetry breaking induced by untwisted fermions in QED in a nonsimply
connected spacetime with topology is investigated. It is
found that the discrete CPT symmetry of the theory is spontaneously broken by
the appearance of a constant vacuum expectation value of the electromagnetic
potential along the direction of space periodicity. The constant potential is
shown to be gauge nonequivalent to zero in the nonsimply connected spacetime
under consideration. Due to the symmetry breaking, one of the electromagnetic
modes of propagation is massive with a mass that depends on the inverse of the
compactification length. As a result, the system exhibits a sort of topological
directional superconductivity.Comment: 6 pages, revte
Zero-conductance resonances and spin-filtering effects in ring conductors subject to Rashba coupling
We investigate the effect of Rashba spin-orbit coupling and of a tunnel
barrier on the zero conduc- tance resonances appearing in a one-dimensional
conducting Aharonov-Bohm (AB) ring symmet- rically coupled to two leads. The
transmission function of the corresponding one-electron problem is derived
within the scattering matrix approach and analyzed in the complex energy plane
with focus on the role of the tunnel barrier strength on the zero-pole
structure characteristic of trans- mission (anti)resonances. The lifting of the
real conductance zeros is related to the breaking of the spin-reversal symmetry
and time-reversal symmetry of Aharonov-Casher (AC)and AB rings, as well as to
rotational symmetry breaking in presence of a tunnel barrier. We show that the
polarization direction of transmitted electrons can be controlled via the
tunnel barrier strength and discuss a novel spin-filtering design in
one-dimensional rings with tunable spin-orbit interaction.Comment: 13 pages, 8 figure
Persistent spin and charge currents and magnification effects in open ring conductors subject to Rashba coupling
We analyze the effect of Rashba spin-orbit coupling and of a local tunnel
barrier on the persistent spin and charge currents in a one-dimensional
conducting Aharonov-Bohm (AB) ring symmetrically coupled to two leads. First,
as an important consequence of the spin-splitting, it is found that a
persistent spin current can be induced which is not simply proportional to the
charge current. Second, a magnification effect of the persistent spin current
is shown when one tunes the Fermi energy near the Fano-type antiresonances of
the total transmission coefficient governed by the tunnel barrier strength. As
an unambiguous signature of spin-orbit coupling we also show the possibility to
produce a persistent pure spin current at the interference zeros of the
transmittance. This widens the possibilities of employing mesoscopic conducting
rings in phase-coherent spintronics applications.Comment: 6 pages, 5 figures, to appear in PR
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The effect of working parameters upon elastohydrodynamic film thickness under periodic load variation
There are a number of widely used machine components, such as rolling element bearings, gears and cams, which operate in the lubrication regime known as Elastohydrodynamics (EHD), where lubricant film thickness is governed by hydrodynamic action of convergent geometry, elastic deformation between non-conformal contacting surfaces, and the increase of lubricant viscosity with pressure. Variable loading conditions occur not only in all the machine components mentioned above, but also in natural joints such as hip or knee joints of humans or many vertebrates. Experimental studies of the behaviour of EHD films under variable loading are scarce and to authors’ knowledge systematic studies of the evolution of lubricant film thickness in EHD contacts subjected to forced harmonic variation of load are even less common. The aim of the present study is to explore the effect of load amplitude on the EHD film behaviour. This is done in alternating cycles with the load varying about a fixed, preset value at various amplitudes. Experimental results are compared with a simple theoretical analysis based on the speed of change of contact’s dimensions, a semi-analytical solution which includes both speed variation and squeeze effect, and finally with a full numerical solution
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