4,552 research outputs found
Multifractality of quantum wave functions in the presence of perturbations
We present a comprehensive study of the destruction of quantum
multifractality in the presence of perturbations. We study diverse
representative models displaying multifractality, including a pseudointegrable
system, the Anderson model and a random matrix model. We apply several types of
natural perturbations which can be relevant for experimental implementations.
We construct an analytical theory for certain cases, and perform extensive
large-scale numerical simulations in other cases. The data are analyzed through
refined methods including double scaling analysis. Our results confirm the
recent conjecture that multifractality breaks down following two scenarios. In
the first one, multifractality is preserved unchanged below a certain
characteristic length which decreases with perturbation strength. In the second
one, multifractality is affected at all scales and disappears uniformly for a
strong enough perturbation. Our refined analysis shows that subtle variants of
these scenarios can be present in certain cases. This study could guide
experimental implementations in order to observe quantum multifractality in
real systems.Comment: 20 pages, 27 figure
Two scenarios for quantum multifractality breakdown
We expose two scenarios for the breakdown of quantum multifractality under
the effect of perturbations. In the first scenario, multifractality survives
below a certain scale of the quantum fluctuations. In the other one, the
fluctuations of the wave functions are changed at every scale and each
multifractal dimension smoothly goes to the ergodic value. We use as generic
examples a one-dimensional dynamical system and the three-dimensional Anderson
model at the metal-insulator transition. Based on our results, we conjecture
that the sensitivity of quantum multifractality to perturbation is universal in
the sense that it follows one of these two scenarios depending on the
perturbation. We also discuss the experimental implications.Comment: 5 pages, 4 figures, minor modifications, published versio
Anomalía congénita del atlas asociada con fractura de la apófisis espinosa de C-7 : a propósito de 1 caso
Se presenta 1 paciente con un defecto congenita del arco posterior del atlas asociado
con una fractura de la apólisis espinosa de C-7. La TAC, precedida de una correcta evaluación
clínica, permiten diferenciar los traumatismos agudos de las anomalías congénitas en el atlas.A case of a congenital cleft of the posterior arch of the atlas associated with a fracture
of the spinous process of C-7 is reported. Appropiate clinical evaluation and CT-scan study
allow to differentiate acute trauma from a congenital abnormality in the atlas
Semiclassical approach to fidelity amplitude
The fidelity amplitude is a quantity of paramount importance in echo type
experiments. We use semiclassical theory to study the average fidelity
amplitude for quantum chaotic systems under external perturbation. We explain
analytically two extreme cases: the random dynamics limit --attained
approximately by strongly chaotic systems-- and the random perturbation limit,
which shows a Lyapunov decay. Numerical simulations help us bridge the gap
between both extreme cases.Comment: 10 pages, 9 figures. Version closest to published versio
Digital Inclusion for Students with Attention Deficit Hyperactivity Disorder
The Attention Deficit Hyperactivity Disorder is a syndrome characterized by distraction, impulsivity, forgetfulness and disorganization. The diagnosis requires considerable care and experience. There are multiples approaches to treatments available, which can be used in combination to meet specific needs. In the academic field, virtual learning environment emerges as a watershed in the life and destiny of students who suffer from the disorder. The objective of this study is to promote digital inclusion for students with ADHD, through a virtual learning environment, in web platform, which will provide tools able to attract attention and stimulate interest in academic activities, aiming to generate significant changes in the process of student development
A declining major merger fraction with redshift in the local Universe from the largest-yet catalog of major and minor mergers in SDSS
It is difficult to accurately identify galaxy mergers and it is an even
larger challenge to classify them by their mass ratio or merger stage. In
previous work we used a suite of simulated mergers to create a classification
technique that uses linear discriminant analysis (LDA) to identify major and
minor mergers. Here, we apply this technique to 1.3 million galaxies from the
SDSS DR16 photometric catalog and present the probability that each galaxy is a
major or minor merger, splitting the classifications by merger stages (early,
late, post-coalescence). We present publicly-available imaging predictor values
and all of the above classifications for one of the largest-yet samples of
galaxies. We measure the major and minor merger fraction ()
and build a mass-complete sample of galaxies, which we bin as a function of
stellar mass and redshift. For the major mergers, we find a positive slope of
with stellar mass and negative slope of
with redshift between stellar masses of
and redshifts of . We are able to reproduce an artificial
positive slope of the major merger fraction with redshift when we do not bin
for mass or craft a complete sample, demonstrating the importance of mass
completeness and mass binning. We determine that the positive trend of the
major merger fraction with stellar mass is consistent with a hierarchical
assembly scenario. The negative trend with redshift requires that an additional
assembly mechanism, such as baryonic feedback, dominates in the local Universe.Comment: 29 pages, 22 figures, see figures 16 and 17 for a summary of the
findings, accepted to MNRA
Life cycle assessment of a vanadium flow battery
The 6th International Conference on Energy and Environment Research, July 22–25, 2019, University of Aveiro, PortugalBattery storage technologies have been showing great potential to address the vulnerability of renewable electricity generation systems. Among the various options, vanadium redox flow batteries are one of the most promising in the energy storage market. In this work, a life cycle assessment of a 5 kW vanadium redox flow battery is performed on a cradle-to-gate approach with focus on the vanadium electrolytes, since they determine the battery’s storage capacity and can be readjusted and reused indefinitely. The functional unit is 1 kWh stored by the battery. The initial results show that the environmental hotspots reside mainly in the structural and material components of the battery, evidencing the need for alternative or recycled materials, preferably produced locally. Since the quantity of electrolytes determine the amount of storable electricity, an analysis was conducted on the variation of the impacts with the increase of storage capacity. An alternative scenario with reused electrolytes was also performed. Results show that with the increase of storage capacity, the contribution of the electrolytes to the impacts decrease significantly by stored kWh. In the reused electrolytes scenario, impacts were reduced mainly for the Acidification and Mineral, fossil and renewable resource depletion categories.This work was financial supported by projects “SunStorage – Harvesting and storage of solar energy”, with reference POCI-01-0145-FEDER-016387, funded by European Regional Development Fund (ERDF), through COMPETE 2020 – Operational Programme for Competitiveness and Internationalization (OPCI), and to FCT — Fundação para a Ciência e a Tecnologia, Portugal I.P., project IF/01093/2014/CP1249/CT0003, research grants IF/01093/2014 and SFRH/BPD/112003/2015. Support from POCI-01-0145-FEDER-006939 (Laboratory for Process Engineering, Environment, Biotechnology and Energy — LEPABE, UID/EQU/00511/2019) funded by FEDER, Spain through COMPETE2020-POCI and by national funds through FCT/MCTES (PIDDAC), Portugal.info:eu-repo/semantics/publishedVersio
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