Forecasting Large Realized Covariance Matrices: The Benefits of Factor Models and Shrinkage

We propose a model to forecast large realized covariance matrices of returns, applying it to the constituents of the S\&P 500 daily. To address the curse of dimensionality, we decompose the return covariance matrix using standard firm-level factors (e.g., size, value, and profitability) and use sectoral restrictions in the residual covariance matrix. This restricted model is then estimated using vector heterogeneous autoregressive (VHAR) models with the least absolute shrinkage and selection operator (LASSO). Our methodology improves forecasting precision relative to standard benchmarks and leads to better estimates of minimum variance portfolios

Copper catalyzed cross-coupling reactions of diaryl ditellurides with potassium aryltrifluoroborate salts

We present here results of the cross-coupling reaction of diaryl ditellurides with potassium aryltrifluoroborate salts using a catalytic amount of Cu(OAc)2 and bypiridine in DMSO/H2O under air atmosphere. This cross-coupling reaction is general and was performed with diaryl ditellurides and potassium aryltrifluoroborate salts bearing electron-withdrawing, electron-donating and neutral substituents, affording the corresponding unsymmetrical diaryl tellurides in good to excellent yields.Apresentamos aqui resultados das reações de acoplamento de diteluretos de diarila com sais de ariltrifluoroborato de potássio, usando quantidades catalíticas de Cu(OAc)2 e bipiridina, em uma mistura de DMSO/H2O, sob ar atmosférico. Estas reações de acoplamento são gerais e são realizadas com diteluretos de diarila e sais de ariltrifluoroborato de potássio contendo substituintes neutros, retiradores e doadores de elétrons, fornecendo os correspondentes teluretos de diarila não simétricos em rendimentos de bons a excelentes.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) (Grants 07/56659-0 and 07/59404-2

Casimir force between integrable and chaotic pistons

We have computed numerically the Casimir force between two identical pistons inside a very long cylinder, considering different shapes for the pistons. The pistons can be considered as quantum billiards, whose spectrum determines the vacuum force. The smooth part of the spectrum fixes the force at short distances, and depends only on geometric quantities like the area or perimeter of the piston. However, correcting terms to the force, coming from the oscillating part of the spectrum which is related to the classical dynamics of the billiard, are qualitatively different for classically integrable or chaotic systems. We have performed a detailed numerical analysis of the corresponding Casimir force for pistons with regular and chaotic classical dynamics. For a family of stadium billiards, we have found that the correcting part of the Casimir force presents a sudden change in the transition from regular to chaotic geometries.Comment: 13 pages, 10 figure

Revisión de las localidades fosilíferas del Grupo Bauru (Cretácico Superior) en la región de Pontal do Triângulo Mineiro (Minas Gerais, Brasil)

La región denominada Pontal do Triângulo Mineiro (PTM) comprende un área que se encuentra en el extremo suroeste del estado de Minas Gerais, Brasil. Los excelentes afloramientos del Grupo Bauru (Cuenca Bauru, Cretácico Superior) son conocidos desde principios del siglo pasado. Sin embargo, son pocos los estudios paleontológicos que se llevaron a cabo de manera sistemática, en comparación con las regiones próximas a Uberaba (Peirópolis) y al oeste de Estado de São Paulo. Este trabajo tiene como objetivo examinar y registrar todos los depósitos fosilíferos de vertebrados en la región de PTM y su contenido de vertebrados fósiles. Los principales afloramientos de la región fueron fotografiados, mapeados a escala 1:100.000 y georeferenciados. La literatura geológica describe una amplia distribución de la Formación Adamantina (Turoniano-Santoniano) en PTM. Los afloramientos principales de esta unidad se encuentran en las localidades de Campina Verde (tres sitios), Carneirinho (dos sitios), Iturama (un sitio) y Prata (tres sitios). La distribución de los sedimentos de la Formación Marília en el PTM es poco representativa, concentrándose principalmente en la localidad de Monte Alegre de Minas. Trabajos de campo realizados durante el 2010 en las ciudades de Capinópolis (un sitio) e Ituiutaba (un sitio) reportaron por primera vez restos indeterminados de vertebrados para la Formación Marília. El registro de vertebrados fósiles de la Formación Adamantina en el PTM está representado por el tiranosaurio Maxakalisaurus topai Kellner, Campos, Azevedo, Trotta, Henriques, Craik y Silva (en la localidad Prata), restos de Crocodylomorpha Sphagesauridae (en Iturama), varios restos de saurópodos y fragmentos indeterminados de vertebrados. La región del PTM, con once sitios fosilíferos, se destaca como un área prometedora para la investigación paleontológica en Minas Gerais.Sesiones libresFacultad de Ciencias Naturales y Muse

Elucidating how the saprophytic fungus Aspergillus nidulans uses the plant polyester suberin as carbon source

Lipid polymers in plant cell walls, such as cutin and suberin, build recalcitrant hydrophobic protective barriers. Their degradation is of foremost importance for both plant pathogenic and saprophytic fungi. Regardless of numerous reports on fungal degradation of emulsified fatty acids or cutin, and on fungi-plant interactions, the pathways involved in the degradation and utilisation of suberin remain largely overlooked. As a structural component of the plant cell wall, suberin isolation, in general, uses harsh depolymerisation methods that destroy its macromolecular structure. We recently overcame this limitation isolating suberin macromolecules in a near-native state.work partially supported by a grant from Iceland, Liechtenstein and Norway through the EEA financial mechanism (Project PT015), FCT: grant (PEst-OE/EQB/LA0004/2013) and fellowships (SFRH/BD/38378/2007, SFRH/BD/66396/2009, SFRH/BD/66030/2009, SFRH/BD/48286/2008), Fundação Calouste Gulbenkian fellowship (21-95587-B)

P2X7 Receptor-Dependent microRNA Expression Profile in the Brain Following Status Epilepticus in Mice

The ionotropic ATP-gated P2X7 receptor is an important contributor to inflammatory signaling cascadesviathe release of Interleukin-1 beta, as well as having roles in cell death, neuronal plasticity and the release of neurotransmitters. Accordingly, there is interest in targeting the P2X7 receptor for the treatment of epilepsy. However, the signaling pathways downstream of P2X7 receptor activation remain incompletely understood. Notably, recent studies showed that P2X7 receptor expression is controlled, in part, by microRNAs (miRNAs). Here, we explored P2X7 receptor-dependent microRNA expression by comparing microRNA expression profiles of wild-type (wt) and P2X7 receptor knockout mice before and after status epilepticus. Genome-wide microRNA profiling was performed using hippocampi from wt and P2X7 receptor knockout mice following status epilepticus induced by intra-amygdala kainic acid. This revealed that the genetic deletion of the P2X7 receptor results in distinct patterns of microRNA expression. Specifically, we found that in vehicle-injected control mice, the lack of the P2X7 receptor resulted in the up-regulation of 50 microRNAs and down-regulation of 35 microRNAs. Post-status epilepticus, P2X7 receptor deficiency led to the up-regulation of 44 microRNAs while 13 microRNAs were down-regulated. Moreover, there was only limited overlap among identified P2X7 receptor-dependent microRNAs between control conditions and post-status epilepticus, suggesting that the P2X7 receptor regulates the expression of different microRNAs during normal physiology and pathology. Bioinformatic analysis revealed that genes targeted by P2X7 receptor-dependent microRNAs were particularly overrepresented in pathways involved in intracellular signaling, inflammation, and cell death;processes that have been repeatedly associated with P2X7 receptor activation. Moreover, whereas genes involved in signaling pathways and inflammation were common among up- and down-regulated P2X7 receptor-dependent microRNAs during physiological and pathological conditions, genes associated with cell death seemed to be restricted to up-regulated microRNAs during both physiological conditions and post-status epilepticus. Taken together, our results demonstrate that the P2X7 receptor impacts on the expression profile of microRNAs in the brain, thereby possibly contributing to both the maintenance of normal cellular homeostasis and pathological processes

The Solar Twin Planet Search: The age-chromospheric activity relation

Context. It is well known that the magnetic activity of solar-type stars decreases with age, but it is widely debated in the literature whether there is a smooth decline or if there is an early sharp drop until 1-2 Gyr that is followed by a relatively inactive constant phase. Aims. We revisited the activity-age relation using time-series observations of a large sample of solar twins whose precise isochronal ages and other important physical parameters have been determined. Methods. We measured the Ca II H and K activity indices using ≈ 9000 HARPS spectra of 82 solar twins. In addition, the average solar activity was calculated through asteroids and Moon reflection spectra using the same instrumentation. Thus, we transformed our activity indices into the S Mount Wilson scale (SMW), recalibrated the Mount Wilson absolute flux and photospheric correction equations as a function of Teff, and then computed an improved bolometric flux normalized activity index log R′HK (Teff) for the entire sample. Results. New relations between activity and the age of solar twins were derived by assessing the chromospheric age-dating limits using log R′HK (Teff). We measured an average solar activity of SMW = 0.1712 ± 0.0017 during solar magnetic cycles 23-24 covered by HARPS observations, and we also inferred an average of SMW = 0.1694 ± 0.0025 for cycles 10-24, anchored on a sunspot number correlation of S index versus. We also found a simple relation between the average and the dispersion of the activity levels of solar twins. This enabled us to predict the stellar variability effects on the age-activity diagram, and consequently, to estimate the chromospheric age uncertainties that are due to the same phenomena. The age-activity relation is still statistically significant up to ages around 6-7 Gyr, in agreement with previous works using open clusters and field stars with precise ages. Conclusions. Our research confirms that Ca II H & K lines remain a useful chromospheric evolution tracer until stars reach ages of at least 6-7 Gyr. We found evidence that for the most homogenous set of old stars, the chromospheric activity indices seem to continue to decrease after the solar age toward the end of the main sequence. Our results indicate that a significant part of the scatter observed in the age-activity relation of solar twins can be attributed to stellar cycle modulations effects. The Sun seems to have a normal activity level and variability for its age.DLO acknowledges the support from FAPESP (2016/20667-8). JM acknowledges support from FAPESP (2012/24392-2) and CNPq (Productivity Fellowship)

Status of the SIRGAS reference frame: recent developments and new challenges

In accordance with recent developments of the International Association of Geodesy (IAG) and the policies promoted by the Subcommittee on Geodesy of the United Nations Committee of Experts on Global Geospatial Information Management (UN-GGIM), a main goal of the Geodetic Reference System for the Americas (SIRGAS) is the procurement of an integrated regional reference frame. This frame should support the precise determination of geocentric coordinates and also provide a unified physical reference frame for gravimetry, physical heights, and a geoid. The geometric reference frame is determined by a network of about 500 continuously operating GNSS stations, which are routinely processed by ten analysis centers. The GNSS solutions from the analysis centers are used to generate weekly station positions aligned to the International Terrestrial Reference Frame (ITRF) and multi-year (cumulative) reference frame solutions. This processing is also the basis for the generation of precise tropospheric zenith path delays with an hourly sampling rate over the Americas. The reference frame for the determination of physical heights is a regional densification of the International Height Reference Frame (IHRF). Current efforts focus on the estimation and evaluation of potential values obtained from high resolution gravity field modelling, an activity tightly coupled with geoid determination. The gravity reference frame aims to be a regional densification of the International Terrestrial Gravity Reference Frame (ITGRF). Thus, SIRGAS activities are focused on evaluating the quality of existing absolute gravity stations and to identify regional gaps where additional absolute gravity stations are needed. Another main goal of SIRGAS is to promote the use of its geodetic reference frame at the national level and to support capacity building activities in the region. This paper summarizes key milestones in the establishment and maintenance of the SIRGAS reference frame and discusses current efforts and future challenges.Fil: Alves Costa, Sonia M.. Instituto Brasileiro de Geografia E Estatística; BrasilFil: Sanchez, Laura. Technische Universität München; AlemaniaFil: Piñon, Diego. Ministerio de Defensa. Instituto Geografico Nacional; ArgentinaFil: Tarrio Mosquera, Jose A.. Universidad de Santiago de Chile; ChileFil: Guimaraes, Gabriel. Universidade Federal de Uberlandia; BrasilFil: Demian Gomez. Ohio University; Estados UnidosFil: Drewes, Hermann. Deutsches Geodätisches Forschungsinstitut; AlemaniaFil: Mackern Oberti, María Virginia. Universidad Nacional de Cuyo. Facultad de Ingeniería; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Antokoletz, Ezequiel Darío. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: de Matos, Ana C. O.C. Universidade de Sao Paulo; BrasilFil: Blitzkow, Denizar. Universidade de Sao Paulo; Brasi