ON THE COMPARISON OF TIME SERIES USING SUBSAMPLING

In this paper we propose a procedure based on the subsampling techniques for the comparison of stationary time series that are not necessarily independent. We study a test based on the Euclidean distance between the autocorrelation functions of two series. Consistency of the proposed method is established. We present a Monte Carlo study with the size and the power of the proposed test.

Approximation of supply curves

In this note, we illustrate the computation of the approximation of the supply curves using a one-step basis. We derive the expression for the L2 approximation and propose a procedure for the selection of nodes of the approximation. We illustrate the use of this approach with three large sets of bid curves from European electricity markets

Clustering time series by linear dependency

We present a new way to find clusters in large vectors of time series by using a measure of similarity between two time series, the generalized cross correlation. This measure compares the determinant of the correlation matrix until some lag k of the bivariate vector with those of the two univariate time series. A matrix of similarities among the series based on this measure is used as input of a clustering algorithm. The procedure is automatic, can be applied to large data sets and it is useful to find groups in dynamic factor models. The cluster method is illustrated with some Monte Carlo experiments and a real data example

Orbital-Free Molecular Dynamics Simulations of Melting in Na8 and Na20: Melting in Steps

The melting-like transitions of Na8 and Na20 are investigated by ab initio constant energy molecular dynamics simulations, using a variant of the Car-Parrinello method which employs an explicit electronic kinetic energy functional of the density, thus avoiding the use of one-particle orbitals. Several melting indicators are evaluated in order to determine the nature of the various transitions, and compared with other simulations. Both Na8 and Na20 melt over a wide temperature range. For Na8, a transition is observed to begin at approx. 110 K, between a rigid phase and a phase involving isomerizations between the different permutational isomers of the ground state structure. The ``liquid'' phase is completely established at approx. 220 K. For Na20, two transitions are observed: the first, at approx. 110 K, is associated with isomerization transitions between those permutational isomers of the ground state structure which are obtained by interchanging the positions of the surface-like atoms; the second, at approx. 160 K, involves a structural transition from the ground state isomer to a new set of isomers with the surface molten. The cluster is completely ``liquid'' at approx. 220 K.Comment: Revised version, accepted for publication in J. Chem. Phys. The changes include longer simulations for the Na20 microcluster, a more complete comparison to previous theoretical results, and the discussion of some technical details of the method applie

A Patterned Architecture of Monoaminergic Afferents in the Cerebellar Cortex: Noradrenergic and Serotonergic Fibre Distributions within Lobules and Parasagittal Zones

The geometry of the glutamatergic mossy-parallel fibre and climbing fibre inputs to cerebellar cortical Purkinje cells has powerfully influenced thinking about cerebellar functions. The compartmentation of the cerebellum into parasagittal zones, identifiable in olivo-cortico-nuclear projections, and the trajectories of the parallel fibres, transverse to these zones and following the long axes of the cortical folia, are particularly important. Two monoaminergic afferent systems, the serotonergic and noradrenergic, are major inputs to the cerebellar cortex but their architecture and relationship with the cortical geometry are poorly understood. Immunohistochemistry for the serotonin transporter (SERT) and for the noradrenaline transporter (NET) revealed strong anisotropy of these afferent fibres in the molecular layer of rat cerebellar cortex. Individual serotonergic fibres travel predominantly medial-lateral, along the long axes of the cortical folia, similar to parallel fibres and Zebrin II immunohistochemistry revealed that they can influence multiple zones. In contrast, individual noradrenergic fibres run predominantly parasagittally with rostral-caudal extents significantly longer than their medial-lateral deviations. Their local area of influence has similarities in form and size to those of identified microzones. Within the molecular layer, the orthogonal trajectories of these two afferent systems suggest different information processing. An individual serotonergic fibre must influence all zones and microzones within its medial-lateral trajectory. In contrast, noradrenergic fibres can influence smaller cortical territories, potentially as limited as a microzone. Evidence is emerging that these monoaminergic systems may not supply a global signal to all of their targets and their potential for cerebellar cortical functions is discussed

The COVID-19 Sentinel Schools Network of Catalonia (CSSNC) project: Associated factors to prevalence and incidence of SARS-CoV-2 infection in educational settings during the 2020–2021 academic year

COVID-19; Medical risk factors; Virus testingCOVID-19; Factors de risc mèdics; Test de virusCOVID-19; Factores de riesgo médicos; Test de virusThe Sentinel Schools project was designed to monitor and evaluate the epidemiology of COVID-19 in Catalonia, gathering evidence for health and education policies to inform the development of health protocols and public health interventions to control of SARS-CoV-2 infection in schools. The aim of this study was to estimate the prevalence and incidence of SARS-CoV-2 infections and to identify their determinants among students and staff during February to June in the academic year 2020–2021. We performed two complementary studies, a cross-sectional and a longitudinal component, using a questionnaire to collect nominal data and testing for SARS-CoV-2 detection. We describe the results and perform a univariate and multivariate analysis. The initial crude seroprevalence was 14.8% (95% CI: 13.1–16.5) and 22% (95% CI: 18.3–25.8) for students and staff respectively, and the active infection prevalence was 0.7% (95% CI: 0.3–1) and 1.1% (95% CI: 0.1–2). The overall incidence for persons at risk was 2.73 per 100 person-month and 2.89 and 2.34 per 100 person-month for students and staff, respectively. Socioeconomic, self-reported knowledge, risk perceptions and contact pattern variables were positively associated with the outcome while sanitary measure compliance was negatively associated, the same significance trend was observed in multivariate analysis. In the longitudinal component, epidemiological close contact with SARS-CoV-2 infection was a risk factor for SARS-CoV-2 infection while the highest socioeconomic status level was protective as was compliance with sanitary measures. The small number of active cases detected in these schools suggests a low transmission among children in school and the efficacy of public health measures implemented, at least in the epidemiological scenario of the study period. The major contribution of this study was to provide results and evidence that help analyze the transmission dynamic of SARS-CoV-2 and evaluate the associations between sanitary protocols implemented, and measures to avoid SARS-CoV-2 spread in schools

A Fast 0.5 T Prepolarizer Module for Preclinical Magnetic Resonance Imaging

We present a magnet and high power electronics for Prepolarized Magnetic Resonance Imaging (PMRI) in a home-made, special-purpose preclinical system designed for simultaneous visualization of hard and soft biological tissues. The sensitivity of MRI systems grows with field strength, but so do their costs. PMRI can boost the signal-to-noise ratio (SNR) in affordable low-field scanners by means of a long and strong magnetic pulse. However, this must be rapidly switched off prior to the imaging pulse sequence, in timescales shorter than the spin relaxation (or T1) time of the sample. We have operated our prepolarizer at up to 0.5 T and demonstrated enhanced magnetization, image SNR and tissue contrast with PMRI of tap water, an ex vivo mouse brain and food samples. These have T1 times ranging from hundreds of milli-seconds to single seconds, while the preliminary high-power electronics setup employed in this work can switch off the prepolarization field in tens of milli-seconds. In order to make this system suitable for solid-state matter and hard tissues, which feature T1 times as short as 10 ms, we are developing new electronics which can cut switching times to ~ 300 μs. This does not require changes in the prepolarizer module, opening the door to the first experimental demonstration of PMRI on hard biological tissues

Direct transformation of crystalline MoO3_3 into few-layers MoS2_2

We fabricate large-area atomically thin MoS$_2$ layers through the direct transformation of crystalline molybdenum MoS$_2$ (MoO$_3$) by sulfurization at relatively low temperatures. The obtained MoS2 sheets are polycrystalline (~10-20 nm single-crystal domain size) with areas of up to 300x300 um$^2$ with 2-4 layers in thickness and show a marked p-type behaviour. The synthesized films are characterized by a combination of complementary techniques: Raman spectroscopy, X-ray diffraction, transmission electron microscopy and electronic transport measurements.Comment: 6 figures in main text, 2 figures in supp. inf

Enhanced stability in CH3NH3PbI3 hybrid perovskite from mechano-chemical synthesis: structural, microstructural and optoelectronic characterization

Among the hybrid organic–inorganic perovskites MAPbX3 (MA: methyl-ammonium CH3–NH3+, X = halogen), the triiodide specimen (MAPbI3) is still the material of choice for solar energy applications. Although it is able to absorb light above its 1.6 eV bandgap, its poor stability in humid air atmosphere has been a major drawback for its use in solar cells. However, we discovered that this perovskite can be prepared by ball milling in a straightforward way, yielding specimens with a superior stability. This fact allowed us to take atomic-resolution STEM images for the first time, with sufficient quality to unveil microscopic aspects of this material. We demonstrated full Iodine content, which might be related to the enhanced stability, in a more compact PbI6 framework with reduced unit-cell volume. A structural investigation from neutron powder diffraction (NPD) data of an undeuterated specimen was essential to determine the configuration of the organic MA unit in the 100–298 K temperature range. A phase transition is identified, from the tetragonal structure observed at RT (space group I4/mcm) to an orthorhombic (space group Pnma) phase where the methyl-ammonium organic units are fully localized. Our NPD data reveal that the MA changes are gradual and start before reaching the phase transition. Optoelectronic measurements yield a photocurrent peak at an illumination wavelength of 820 nm, which is redshifted by 30 nm with respect to previously reported measurements on MAPbI3 perovskites synthesized by crystallization from organic solvents.Fil: Lopez, Carlos Alberto. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Área Química General e Inorgánica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Investigaciones en Tecnología Química. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Instituto de Investigaciones en Tecnología Química; ArgentinaFil: Abia, Carmen. Instituto de Ciencia de Materiales de Madrid; España. Institut Laue Langevin; FranciaFil: Rodrigues, Joao E.. Instituto de Ciencia de Materiales de Madrid; EspañaFil: Serrano Sánchez, Federico. Instituto de Ciencia de Materiales de Madrid; EspañaFil: Nemes, Norbert M.. Instituto de Ciencia de Materiales de Madrid; EspañaFil: Martínez, José L.. Instituto de Ciencia de Materiales de Madrid; EspañaFil: Fernandez Díaz, María T.. Institut Laue Langevin; FranciaFil: Biškup, Neven. Universidad Complutense de Madrid; EspañaFil: Alvarez Galván, Consuelo. Consejo Superior de Investigaciones Científicas; EspañaFil: Carrascoso, Felix. Instituto de Ciencia de Materiales de Madrid; EspañaFil: Castellanos Gomez, Andres. Instituto de Ciencia de Materiales de Madrid; EspañaFil: Alonso, José A.. Instituto de Ciencia de Materiales de Madrid; Españ