15,087 research outputs found
Paramagnetic excited vortex states in superconductors
We consider excited vortex states, which are vortex states left inside a
superconductor once the external applied magnetic field is switched off and
whose energy is lower than of the normal state. We show that this state is
paramagnetic and develop here a general method to obtain its Gibbs free energy
through conformal mapping. The solution for any number of vortices in any cross
section geometry can be read off from the Schwarz - Christoffel mapping. The
method is based on the first order equations used by A. Abrikosov to discover
vortices.Comment: 14 pages, 7 figure
Vacuum fluctuations of a scalar field near a reflecting boundary and their effects on the motion of a test particle
The contribution from quantum vacuum fluctuations of a real massless scalar
field to the motion of a test particle that interacts with the field in the
presence of a perfectly reflecting flat boundary is here investigated. There is
no quantum induced dispersions on the motion of the particle when it is alone
in the empty space. However, when a reflecting wall is introduced, dispersions
occur with magnitude dependent on how fast the system evolves between the two
scenarios. A possible way of implementing this process would be by means of an
idealized sudden switching, for which the transition occurs instantaneously.
Although the sudden process is a simple and mathematically convenient
idealization it brings some divergences to the results, particularly at a time
corresponding to a round trip of a light signal between the particle and the
wall. It is shown that the use of smooth switching functions, besides
regularizing such divergences, enables us to better understand the behavior of
the quantum dispersions induced on the motion of the particle. Furthermore, the
action of modifying the vacuum state of the system leads to a change in the
particle energy that depends on how fast the transition between these states is
implemented. Possible implications of these results to the similar case of an
electric charge near a perfectly conducting wall are discussed.Comment: 17 pages, 8 figure
Transformação estável da linhagem celular BTI-Tn-5B1-4 utilizando o gene 25KFP do baculovirus AgMNPV.
bitstream/CENARGEN/29465/1/bp188.pd
Five-Dimensional QED, Muon Pair Production and Correction to the Coulomb Potential
We consider QED in five dimensions in a configuration where matter is
localized on a 3-brane while foton propagates in the bulk. The idea is to
investigate the effects of the Kaluza-Klein modes of the photon in the
relativistic regime, but in low energy, and in the nonrelativistic regime. In
the relativistic regime, we calculate the cross section for the reaction . We compare our theoretical result with a precise
measurement of this cross section at GeV. As result, we
extract a lower bound on the size of the extra dimension. In the
nonrelativistic regime, we derive the contribution for the Coulomb potential
due to the whole tower of the Kaluza-Klein excited modes of the photon. We use
the modified potential to calculate the Rutherford scattering differential
cross section.Comment: minor changes, three new refs. added, to appear in IJMP
Anisotropic superconducting properties of aligned MgB2 crystallites
Samples of aligned MgB2 crystallites have been prepared, allowing for the
first time the direct identification of an upper critical field anisotropy
Hc2^{ab}/Hc2^{c}= xi_{ab}/xi_{c} ~ 1.73; with xi_{o,ab} ~ 70 A, xi_{o,c} ~ 40
A, and a mass anisotropy ratio m_{ab}/m_{c} ~ 0.3. A ferromagnetic background
signal was identified, possibly related to the raw materials purity.Comment: 4 pages, 4 figures; Revised version to appear in Phys. Rev. Let
- …