1,627 research outputs found
On the effective action of the vacuum photon splitting in Lorentz-violating QED
We consider one-loop radiative corrections from Lorentz- and CPT- violating
extended QED to address the specific problem of finding explicitly an effective
action describing amplitude of photon triple splitting. We show that it is not
possible to find a nonzero photon triple splitting effective action, at least
by using the derivative expansion method (at zero external momenta), up to
leading order in the Lorentz- and CPT- violating parameter.Comment: 4 pages, version to appear in EP
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Characterization of fluid flow in a microchannel with a flow disturbing step
This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.The flow around a flow-disturbing step in a rectangular microchannel is studied by measuring the
wall shear rate along the channel, using the electrodiffusion technique and by determining the velocity field
using the -PIV method. A parametric study based on the Design of Experiments (DOE) and the Response
Surface Methodology (RSM) was then performed, and the effect of key design parameters on the flow characteristics
was numerically investigated using CFD simulations. The computational results are in excellent agreement
with the corresponding experimental ones. The CFD simulations cover both the laminar and the turbulent
flow regime. It was revealed that in both flow regimes the step height has a major influence on the recirculation
length. However, the Reynolds number (Re) value affects the recirculation length only in the laminar region,
while the step length seems to have no significant effect compared to the Re and the step height. Finally, new
correlations are proposed predicting the length of the bottom recirculation zone with reasonable accuracy and
can be used as rough guidelines for the design of microdevices
Violation of the Ikeda sum rule and the self-consistency in the renormalized quasiparticle random phase approximation and the nuclear double-beta decay
The effect of the inclusion of ground state correlations into the QRPA
equation of motion for the two-neutrino double beta () decay
is carefully analyzed. The resulting model, called renormalized QRPA (RQRPA),
does not collapse near the physical value of the nuclear force strength in the
particle-particle channel, as happens with the ordinary QRPA. Still, the
transition amplitude is only slightly less sensitive on
this parameter in the RQRPA than that in the plain QRPA. It is argued that this
fact reveals once more that the characteristic behaviour of the
transition amplitude within the QRPA is not an artifact of
the model, but a consequence of the partial restoration of the spin-isospin
symmetry. It is shown that the price paid for bypassing the collapse in
the RQRPA is the violation of the Ikeda sum rule.Comment: 16 pages, latex, 3 postscript figure
Time-Dependent Variational Analysis of Josephson Oscillations in a Two-component Bose-Einstein Condensate
The dynamics of Josephson-like oscillations between two coupled Bose-Einstein
condensates is studied using the time-dependent variational method. We suppose
that the quantum state of the condensates is a gaussian wave-packet which can
translate and perform breathing shape oscillations. Under this hypotheses we
study the influence of these degrees of freedom on the tunneling dynamics by
comparing the full-model with one where these degrees of freedom are ``frozen''
at its equilibrium values. The result of our calculation shows that when the
traps are not displaced the two models agree, whereas when they are, the models
differ considerably, the former being now closer to its linear approximation.Comment: 10 pages, 2 figure
Electronic Phase Separation Transition as the Origin of the Superconductivity and the Pseudogap Phase of Cuprates
We propose a new phase of matter, an electronic phase separation transition
that starts near the upper pseudogap and segregates the holes into high and low
density domains. The Cahn-Hilliard approach is used to follow quantitatively
this second order transition. The resulting grain boundary potential confines
the charge in domains and favors the development of intragrain superconducting
amplitudes. The zero resistivity transition arises only when the intergrain
Josephson coupling is of the order of the thermal energy and phase
locking among the superconducting grains takes place. We show that this
approach explains the pseudogap and superconducting phases in a natural way and
reproduces some recent scanning tunneling microscopy dataComment: 4 pages and 5 eps fig
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