1,276 research outputs found
Floquet topological transitions in a driven one-dimensional topological insulator
The Su-Schrieffer-Heeger model of polyacetylene is a paradigmatic Hamiltonian
exhibiting non-trivial edge states. By using Floquet theory we study how the
spectrum of this one-dimensional topological insulator is affected by a
time-dependent potential. In particular, we evidence the competition among
different photon-assisted processes and the native topology of the unperturbed
Hamiltonian to settle the resulting topology at different driving frequencies.
While some regions of the quasienergy spectrum develop new gaps hosting Floquet
edge states, the native gap can be dramatically reduced and the original edge
states may be destroyed or replaced by new Floquet edge states. Our study is
complemented by an analysis of Zak phase applied to the Floquet bands. Besides
serving as a simple example for understanding the physics of driven topological
phases, our results could find a promising test-ground in cold matter
experiments
Crafting zero-bias one-way transport of charge and spin
We explore the electronic structure and transport properties of a metal on
top of a (weakly coupled) two-dimensional topological insulator. Unlike the
widely studied junctions between topological non-trivial materials, the systems
studied here allow for a unique bandstructure and transport steering. First,
states on the topological insulator layer may coexist with the gapless bulk
and, second, the edge states on one edge can be selectively switched-off,
thereby leading to nearly perfect directional transport of charge and spin even
in the zero bias limit. We illustrate these phenomena for Bernal stacked
bilayer graphene with Haldane or intrinsic spin-orbit terms and a perpendicular
bias voltage. This opens a path for realizing directed transport in materials
such as van der Waals heterostructures, monolayer and ultrathin topological
insulators.Comment: 7 pages, 7 figure
Jacobsen syndrome and neonatal bleeding: report on two unrelated patients
Introduction: In 1973, Petrea Jacobsen described the first patient showing dysmorphic features, developmental delay and congenital heart disease (atrial and ventricular septal defect) associated to a 11q deletion, inherited from the father. Since then, more than 200 patients have been reported, and the chromosomal critical region responsible for this contiguous gene disorder has been identified. Patients’ presentation: We report on two unrelated newborns observed in Italy affected by Jacobsen syndrome (JBS, also known as 11q23 deletion). Both patients presented prenatal and postnatal bleeding, growth and developmental delay, craniofacial dysmorphisms, multiple congenital anomalies, and pancytopenia of variable degree. Array comparative genomic hybridization (aCGH) identified a terminal deletion at 11q24.1-q25 of 12.5 Mb and 11 Mb, in Patient 1 and 2, respectively. Fluorescent in situ hybridization (FISH) analysis of the parents documented a de novo origin of the deletion for Patient 1; parents of Patient 2 refused further genetic investigations. Conclusions: Present newborns show the full phenotype of JBS including thrombocytopenia, according to their wide 11q deletion size. Bleeding was particularly severe in one of them, leading to a cerebral hemorrhage. Our report highlights the relevance of early diagnosis, genetic counselling and careful management and follow-up of JBS patients, which may avoid severe clinical consequences and lower the mortality risk. It may provide further insights and a better characterization of JBS, suggesting new elements of the genotype-phenotype correlations
Color space distortions in patients with type 2 diabetes mellitus
Color vision impairment was examined in patients with type 2 diabetes mellitus (DM2) without retinopathy. We assessed the type and degree of distortions of individual color spaces. DM2 patients (n = 32), and age-matched controls (n = 20)were tested using the Farnsworth D-15 and the Lanthony D-15d tests. In addition, subsets of caps
from both tests were employed in a triadic procedure (Bimler & Kirkland, 2004). Matrices of inter-cap subjective dissimilarities were estimated from each subject’s “odd-one-out” choices, and processed using non-metric
multidimensional scaling. Two-dimensional color spaces, individual and group (DM2 patients; controls), were reconstructed, with the axes interpreted as the R0G and B0Y perceptual opponent systems. Compared to controls, patient results were not significant for the D-15 and D-15d. In contrast, in the triadic procedure the residual distances were significantly different compared to controls: right eye, P 0.021, and left eye, P 0.022. Color
space configurations for the DM2 patients were compressed along the B0Y and R0G dimensions. The present findings agree with earlier studies demonstrating diffuse losses in early stages of DM2. The proposed method of testing uses color spaces to represent discrimination and provides more differentiated quantitative diagnosis, which
may be interpreted as the perceptual color system affected. In addition, it enables the detection of very mild color vision impairment that is not captured by the D-15d test. Along with fundoscopy, individual color spaces may serve for monitoring early functional changes and thereby to support a treatment strategy
The structure of an endogenous Drosophila centromere reveals the prevalence of tandemly repeated sequences able to form i-motifs
Centromeres are the chromosomal loci at which spindle microtubules attach to mediate chromosome segregation during mitosis and meiosis. In most eukaryotes, centromeres are made up of highly repetitive DNA sequences (satellite DNA) interspersed with middle repetitive DNA sequences (transposable elements). Despite the efforts to establish complete genomic sequences of eukaryotic organisms, the so-called 'finished' genomes are not actually complete because the centromeres have not been assembled due to the intrinsic difficulties in constructing both physical maps and complete sequence assemblies of long stretches of tandemly repetitive DNA. Here we show the first molecular structure of an endogenous Drosophila centromere and the ability of the C-rich dodeca satellite strand to form dimeric i-motifs. The finding of i-motif structures in simple and complex centromeric satellite DNAs leads us to suggest that these centromeric sequences may have been selected not by their primary sequence but by their ability to form noncanonical secondary structures.Peer Reviewe
LAGOVirtual: A Collaborative Environment for the Large Aperture GRB Observatory
We present the LAGOVirtual Project: an ongoing project to develop platform to
collaborate in the Large Aperture GRB Observatory (LAGO). This continental-wide
observatory is devised to detect high energy (around 100 GeV) component of
Gamma Ray Bursts, by using the single particle technique in arrays of Water
Cherenkov Detectors (WCD) at high mountain sites (Chacaltaya, Bolivia, 5300 m
a.s.l., Pico Espejo, Venezuela, 4750 m a.s.l., Sierra Negra, Mexico, 4650 m
a.s.l). This platform will allow LAGO collaboration to share data, and computer
resources through its different sites. This environment has the possibility to
generate synthetic data by simulating the showers through AIRES application and
to store/preserve distributed data files collected by the WCD at the LAGO
sites. The present article concerns the implementation of a prototype of
LAGO-DR adapting DSpace, with a hierarchical structure (i.e. country,
institution, followed by collections that contain the metadata and data files),
for the captured/simulated data. This structure was generated by using the
community, sub-community, collection, item model; available at the DSpace
software. Each member institution-country of the project has the appropriate
permissions on the system to publish information (descriptive metadata and
associated data files). The platform can also associate multiple files to each
item of data (data from the instruments, graphics, postprocessed-data, etc.).Comment: Second EELA-2 Conference Choroni, Venezuela, November 25th to 27th
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Magnitude and determinants of antibiotic dispensing without prescription in Spain: a simulated patient study
Objectives: Excessive and inappropriate use of antibiotics increases antimicrobial resistance. The aim of this study was to determine the magnitude and determinants of antibiotic dispensing without prescription in Spain by the simulated patient technique. Methods: A cross-sectional study was conducted with all the pharmacies in a region of north-west Spain (n = 977), between December 2016 and January 2017. Four actors visited the pharmacies simulating a respiratory infection. Four incremental levels of pressure were used to obtain an antibiotic. The education and sex of the person who was dispensing and the area where the pharmacy was located were recorded. The effect of these independent variables on the dispensing of an antibiotic without prescription (1 = yes, 0 = no) was modelled by logistic regression. Results: An antibiotic was obtained in 18.83% (95% CI = 16.5%-21.41%) of the visits. The area influenced the dispensing of antibiotics without a medical prescription, with a greater likelihood of dispensing in rural (OR = 1.79; 95% CI = 1.20-2.68) or semi-rural (OR = 1.66; 95% CI = 1.13-2.44) areas than in urban areas. No association was found with the sex or the training of the person who dispensed the antibiotic. In the pharmacies in urban areas, a lower level of pressure was needed to obtain the antibiotic. Conclusions: This study shows that one-fifth of the pharmacies still dispense antibiotics without prescription, especially under patient pressure. A rural setting has been identified as a risk factor for dispensing without prescription, so it must be taken into account for future interventions
From cosmic deceleration to acceleration: new constraints from SN Ia and BAO/CMB
We use type Ia supernovae (SN Ia) data in combination with recent baryonic
acoustic oscillations (BAO) and cosmic microwave background (CMB) observations
to constrain a kink-like parametrization of the deceleration parameter ().
This -parametrization can be written in terms of the initial () and
present () values of the deceleration parameter, the redshift of the
cosmic transition from deceleration to acceleration () and the redshift
width of such transition (). By assuming a flat space geometry,
and adopting a likelihood approach to deal with the SN Ia data we obtain, at
the 68% confidence level (C.L.), that: ,
and when we combine
BAO/CMB observations with SN Ia data processed with the MLCS2k2 light-curve
fitter. When in this combination we use the SALT2 fitter we get instead, at the
same C.L.: , and
. Our results indicate, with a quite general and
model independent approach, that MLCS2k2 favors Dvali-Gabadadze-Porrati-like
cosmological models, while SALT2 favors CDM-like ones. Progress in
determining the transition redshift and/or the present value of the
deceleration parameter depends crucially on solving the issue of the difference
obtained when using these two light-curve fitters.Comment: 25 pages, 9 figure
O Sabor das frutas tropicais no Brasil.
Título e texto em português, inglês e espanhol. Títulos equivalentes: The taste of tropical fruits in Brazil = El Sabor de las frutas tropicales en Brasil
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