18,194 research outputs found
One-dimensional relativistic dissipative system with constant force and its quantization
For a relativistic particle under a constant force and a linear velocity
dissipation force, a constant of motion is found. Problems are shown for
getting the Hamiltoninan of this system. Thus, the quantization of this system
is carried out through the constant of motion and using the quantization of the
velocity variable. The dissipative relativistic quantum bouncer is outlined
within this quantization approach.Comment: 11 pages, no figure
Generalized parity transformations in the regularized Chern-Simons theory
We study renormalization effects in the Abelian Chern-Simons (CS) action.
These effects can be non-trivial when the gauge field is coupled to dynamical
matter, since the regularization of the UV divergences in the model forces the
introduction of a parity even piece in the gauge field action. This changes the
classical (odd) transformation properties of the pure CS action. This effect,
already discussed for the case of a lattice regularization by F. Berruto, M.C.
Diamantini and P. Sodano in hep-th/0004203, is also present when the theory is
defined in the continuum and, indeed, it is a manifestation of a more general
`anomalous' effect, since it happens for every regularization scheme. We
explore the physical consequences of this anomaly. We also show that
generalized, nonlocal parity transformations can be defined in such a way that
the regularized theory is odd, and that those transformations tend to the usual
ones when the cutoff is removed. These generalized transformations play a role
that is tantamount to the deformed symmetry corresponding to Ginsparg-Wilson
fermions [2] (in an even number of spacetime dimensions).Comment: 16 pages, LaTeX, references added and typos correcte
From Coulomb blockade to the Kondo regime in a Rashba dot
We investigate the electronic transport in a quantum wire with localized
Rashba interaction. The Rashba field forms quasi-bound states which couple to
the continuum states with an opposite spin direction. The presence of this
Rashba dot causes Fano-like antiresonances and dips in the wire's linear
conductance. The Fano lineshape arises from the interference between the direct
transmission channel along the wire and the hopping through the Rashba dot. Due
to the confinement, we predict the observation of large charging energies in
the local Rashba region which lead to Coulomb-blockade effects in the transport
properties of the wire. Importantly, the Kondo regime can be achieved with a
proper tuning of the Rashba interaction, giving rise to an oscillating linear
conductance for a fixed occupation of the Rashba dot.Comment: 6 pages, 3 figures; presentation improved, discussions extended.
Published versio
Josephson current in strongly correlated double quantum dots
We study the transport properties of a serial double quantum dot (DQD)
coupled to two superconducting leads, focusing on the Josephson current through
the DQD and the associated 0- transitions which result from the subtle
interplay between the superconductivity, the Kondo physics, and the inter-dot
superexchange interaction. We examine the competition between the
superconductivity and the Kondo physics by tuning the relative strength
of the superconducting gap and the Kondo temperature
, for different strengths of the superexchange coupling determined by the
interdot tunneling relative to the dot level broadening . We find
strong renormalization of , a significant role of the superexchange coupling
, and a rich phase diagram of the 0 and -junction regimes. In
particular, when both the superconductivity and the exchange interaction are in
close competion with the Kondo physics (), there appears
an island of -phase at large values of the superconducting phase
difference.Comment: 4 pages, 4 figure
A Sustainable Approach for the Downstream Processing of Bacterial Polyhydroxyalkanoates: State-of-the-art and latest developments
Bioplastics have emerged as a platform to reduce our dependence on fossil fuels. Polyhydroxyalkanoates (PHAs) are a family of biodegradable polyesters with large potential in consumer goods and medical applications. These polymers accumulate in prokaryotic microbes and their recovery is a challenging, often under explored, operation. In the past, oil-derived solvents and chemicals have been widely used as extracting agents, compromising the “environmentally-friendly” claim of bioplastics. Furthermore, the large amount of chemicals and solvents required at the industrial level would negatively impact the economics of the process. The present review presents the latest advances in the field of downstream operations for PHA recovery emphasizing those green technologies with scaling-up feasibility. As for the upstream and fermentation stages, the extraction process needs to be carefully optimized to accomplish a competitive production of PHAs
Impact of noise on a dynamical system: prediction and uncertainties from a swarm-optimized neural network
In this study, an artificial neural network (ANN) based on particle swarm
optimization (PSO) was developed for the time series prediction. The hybrid
ANN+PSO algorithm was applied on Mackey--Glass chaotic time series in the
short-term . The performance prediction was evaluated and compared with
another studies available in the literature. Also, we presented properties of
the dynamical system via the study of chaotic behaviour obtained from the
predicted time series. Next, the hybrid ANN+PSO algorithm was complemented with
a Gaussian stochastic procedure (called {\it stochastic} hybrid ANN+PSO) in
order to obtain a new estimator of the predictions, which also allowed us to
compute uncertainties of predictions for noisy Mackey--Glass chaotic time
series. Thus, we studied the impact of noise for several cases with a white
noise level () from 0.01 to 0.1.Comment: 11 pages, 8 figure
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