4,361 research outputs found
Confinement and Quantization Effects in Mesoscopic Superconducting Structures
We have studied quantization and confinement effects in nanostructured
superconductors. Three different types of nanostructured samples were
investigated: individual structures (line, loop, dot), 1-dimensional (1D)
clusters of loops and 2D clusters of antidots, and finally large lattices of
antidots. Hereby, a crossover from individual elementary "plaquettes", via
clusters, to huge arrays of these elements, is realized. The main idea of our
study was to vary the boundary conditions for confinement of the
superconducting condensate by taking samples of different topology and, through
that, modifying the lowest Landau level E_LLL(H). Since the critical
temperature versus applied magnetic field T_c(H) is, in fact, E_LLL(H) measured
in temperature units, it is varied as well when the sample topology is changed
through nanostructuring. We demonstrate that in all studied nanostructured
superconductors the shape of the T_c(H) phase boundary is determined by the
confinement topology in a unique way.Comment: 28 pages, 19 EPS figures, uses LaTeX's aipproc.sty, contribution to
Euroschool on "Superconductivity in Networks and Mesoscopic Systems", held in
Siena, Italy (8-20 september 1997
Can we always get the entanglement entropy from the Kadanoff-Baym equations? The case of the T-matrix approximation
We study the time-dependent transmission of entanglement entropy through an
out-of-equilibrium model interacting device in a quantum transport set-up. The
dynamics is performed via the Kadanoff-Baym equations within many-body
perturbation theory. The double occupancy , needed to determine the entanglement entropy, is obtained from
the equations of motion of the single-particle Green's function. A remarkable
result of our calculations is that can become negative, thus not permitting to evaluate the
entanglement entropy. This is a shortcoming of approximate, and yet conserving,
many-body self-energies. Among the tested perturbation schemes, the -matrix
approximation stands out for two reasons: it compares well to exact results in
the low density regime and it always provides a non-negative . For the second part of this statement, we
give an analytical proof. Finally, the transmission of entanglement across the
device is diminished by interactions but can be amplified by a current flowing
through the system.Comment: 6 pages, 6 figure
Unusual magneto-transport of YBa2Cu3O7-d films due to the interplay of anisotropy, random disorder and nanoscale periodic pinning
We study the general problem of a manifold of interacting elastic lines whose
spatial correlations are strongly affected by the competition between random
and ordered pinning. This is done through magneto-transport experiments with
YBa2Cu3O7-d thin films that contain a periodic vortex pinning array created via
masked ion irradiation, in addition to the native random pinning. The strong
field-matching effects we observe suggest the prevalence of periodic pinning,
and indicate that at the matching field each vortex line is bound to an
artificial pinning site. However, the vortex-glass transition dimensionality,
quasi-2D instead of the usual 3D, evidences reduced vortex-glass correlations
along the vortex line. This is also supported by an unusual angular dependence
of the magneto-resistance, which greatly differs from that of Bose-glass
systems. A quantitative analysis of the angular magnetoresistance allows us to
link this behaviour to the enhancement of the system anisotropy, a collateral
effect of the ion irradiation
Giant vortex state in perforated aluminum microsquares
We investigate the nucleation of superconductivity in a uniform perpendicular
magnetic field H in aluminum microsquares containing a few (2 and 4) submicron
holes (antidots). The normal/superconducting phase boundary T_c(H) of these
structures shows a quite different behavior in low and high fields. In the low
magnetic field regime fluxoid quantization around each antidot leads to
oscillations in T_c(H), expected from the specific sample geometry, and
reminiscent of the network behavior. In high magnetic fields, the T_c(H)
boundaries of the perforated and a reference non-perforated microsquare reveal
cusps at the same values of Phi/Phi_0 (where Phi is the applied flux threading
the total square area and Phi_0 is the superconducting flux quantum), while the
background on T_c(H) becomes quasi-linear, indicating that a giant vortex state
is established. The influence of the actual geometries on T_c(H) is analyzed in
the framework of the linearized Ginzburg-Landau theory.Comment: 14 pages, 6 PS figures, RevTex, accepted for publication in Phys.
Rev.
Kadanoff-Baym approach to time-dependent quantum transport in AC and DC fields
We have developed a method based on the embedded Kadanoff-Baym equations to
study the time evolution of open and inhomogeneous systems. The equation of
motion for the Green's function on the Keldysh contour is solved using
different conserving many-body approximations for the self-energy. Our
formulation incorporates basic conservation laws, such as particle
conservation, and includes both initial correlations and initial embedding
effects, without restrictions on the time-dependence of the external driving
field. We present results for the time-dependent density, current and dipole
moment for a correlated tight binding chain connected to one-dimensional
non-interacting leads exposed to DC and AC biases of various forms. We find
that the self-consistent 2B and GW approximations are in extremely good
agreement with each other at all times, for the long-range interactions that we
consider. In the DC case we show that the oscillations in the transients can be
understood from interchain and lead-chain transitions in the system and find
that the dominant frequency corresponds to the HOMO-LUMO transition of the
central wire. For AC biases with odd inversion symmetry odd harmonics to high
harmonic order in the driving frequency are observed in the dipole moment,
whereas for asymmetric applied bias also even harmonics have considerable
intensity. In both cases we find that the HOMO-LUMO transition strongly mixes
with the harmonics leading to harmonic peaks with enhanced intensity at the
HOMO-LUMO transition energy.Comment: 16 pages, 9 figures. Submitted at "Progress in Nonequilibrium Green's
Functions IV" conferenc
A Nonperturbative Eliasson's Reducibility Theorem
This paper is concerned with discrete, one-dimensional Schr\"odinger
operators with real analytic potentials and one Diophantine frequency. Using
localization and duality we show that almost every point in the spectrum admits
a quasi-periodic Bloch wave if the potential is smaller than a certain constant
which does not depend on the precise Diophantine conditions. The associated
first-order system, a quasi-periodic skew-product, is shown to be reducible for
almost all values of the energy. This is a partial nonperturbative
generalization of a reducibility theorem by Eliasson. We also extend
nonperturbatively the genericity of Cantor spectrum for these Schr\"odinger
operators. Finally we prove that in our setting, Cantor spectrum implies the
existence of a -set of energies whose Schr\"odinger cocycle is not
reducible to constant coefficients
10th IFAC Symposium for Fault Detection, Supervision and Safety for Technical Processes
Producción CientíficaThis paper addresses the problem of leak localization in water distribution networks (WDN)
using Fisher Discriminant Analysis (FDA). First, the paper introduces how FDA can be used for leak
localization using the information of pressure measurements from the sensors available in the WDN. Then, the problem of sensor placement is considered when the proposed leak localization based on FDA is used. The proposed leak localization and sensor placement approaches based on FDA will be used using a well-known WDN case study.Este trabajo forma parte del proyecto de investigación: MINECO/FEDER: DPI2015-67341-C2-2-R
Mediation of perceived stress and cortisol in the association between neuroticism and global cognition in older adults: A longitudinal study
Neuroticism has been associated with a greater dementia risk, but its association with cognitive decline in healthy older adults remains unclear. Stress has been proposed as one of the mechanisms that could explain this relationship. Our aim was to analyse, in healthy older people, the mediating role of perceived stress and the Hypothalamic–Pituitary–Adrenal (HPA) axis in the association between neuroticism and global cognition. At Waves 1 and 2 (4-year follow-up), 87 older people (49.4% women; M age = 65.08, SD = 4.54 at Wave 1) completed a neuropsychological battery and the Perceived Stress Scale (PSS), and provided saliva samples on two (Wave 1) and three (Wave 2) consecutive days to measure the wake-to-bed slope. In Wave 2, neuroticism was assessed with the NEO-Five-Factor Inventory. PSS, but not the wake-to-bed slope, mediated the negative associations between neuroticism and global cognition (Waves 1, 2 and change). Regarding gender differences, PSS (Waves 1, 2 and change) and the wake-to-bed slope (Wave 2 and change) mediated these associations in men. Our results suggest that perceived stress and HPA-axis dysregulation could act as mechanisms underlying the association between neuroticism and cognitive functioning and decline, at least in older men. © 2021. The Authors. Stress and Health published by John Wiley & Sons Ltd
Growing monitoring in sea cages: TS measurements issues
Hydroacoustic monitoring of fish growing in sea cages needs of an accurate
relationship between fish size and target strength (TS) for every species of commercial
interest. We discuss the conditions for TS measurement in near range conditions in sea
cages for the case of the dorsal and ventral aspects of gilthead
sea bream and bluefin
tuna.
Gilthead sea bream dorsal and ventral TS distributions, obtained with a split beam
echosounder, are unimodal
and the same results are derived for single beam data
analysis when specific processing threshold criteria are applied. The expected linear
relationship between the average TS and the logarithm of fish length is only found for
the ventral case, being more accurate the uncompensated TS single beam analysis,
probably due to near range errors.
Bluefin tuna dorsal measurements performed in a fattening farm from February to July
did not show a significant variation of TS distributions, and we propose a synchronized
system of echosounder and video recordings, in order to relate target strength and
orientation and size of specific tuna in the acoustic beam. Preliminary results indicate
that only ventral TS values correlate properly with tuna size
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