Diagnosing order by disorder in quantum spin systems

In this paper we study the frustrated J1-J2 quantum Heisenberg model on the square lattice for J2 > 2J1, in a magnetic field. In this regime the classical system is known to have a degenerate manifold of lowest energy configurations, where standard thermal order by disorder occurs. In order to study its quantum version we use a path integral formulation in terms of coherent states. We show that the classical degeneracy in the plane transverse to the magnetic field is lifted by quantum fluctuations. Collinear states are then selected, in a similar pattern to that set by thermal order by disorder, leaving a Z2 degeneracy. A careful analysis reveals a purely quantum mechanical effect given by the tunneling between the two minima selected by fluctuations. The effective description contains two planar (XY -like) fields conjugate to the total magnetization and the difference of the two sublattice magnetizations. Disorder in either or both of these fields produces the locking of their conjugate observables. Furthermore, within this scenario we argue that the quantum state is close to a product state.Comment: 8 pages, 3 figure

Coastal bathymetry estimation using an ensemble of synthetic aperture radar images from Sentinel-1

In this study, coastal bathymetry is estimated with a wave ray-tracing algorithm using wave parameters retrieved from Synthetic Aperture Radar (SAR) images acquired by the Sentinel-1 satellites. The method relies on the long swell wave’s detection by SAR imagery and the wave’s properties adjustment to the underwater topography, which can be mathematically related using the linear dispersion relation. The ray-tracing algorithm tracks the shoaling waves until the wave breaking zone, using the wavelength and wave direction retrieved from the 2D directional spectra applied at consecutive sub-images. Then, by inverting the linear wave dispersion relationship, the depth is calculated based on the mean wavelength obtained for each sub-image and maintaining the wave period retrieved at the first offshore position, which is computed using a mean depth from an independent bathymetric source. The output of the algorithm is a bathymetric model that results from the interpolation of the depth computed at each tracking position to a uniform grid and the results are compared with bathymetric information from the General Bathymetric Chart of the Ocean. The use of a monthly ensemble of SAR images, instead of individual ones, to reproduce the bathymetry near Aveiro, Portugal, resulted in a smoother topography with lower relative errors, suggesting that the final bathymetric model retrieved from SAR should result from a combination of SAR images. The methodology presented here to infer the bathymetry using space-borne SAR imagery can be useful to retrieve the mean bottom topography (especially in remote areas where the traditional hydrographic surveying methods are not performed regularly) and to reproduce new underwater structures, such as banks, reefs or bars, which are important to detect for the safety of navigation.Peer Reviewe

SOLAR SOFTWARE APPLIED TO DESIGN A PHOTOVOLTAIC SYSTEM TO SUPPLY THE ENERGY DEMAND OF AN ITALIAN SCHOOL

This paper has as objective to describe the use of SOLAR 1.1 software todesign a system for supplying a part of the electric demand of a schoolsituated in Umbertide, comparing the use o SOLAR 1.1 to real results of asystem implanted yet. This software version helps also to conduce theeconomic analysis for grid connected or standalone photovoltaic systemsfor the choice of convenient values of investment rate and annuity factorand it calculates the payback period of investment in the photovoltaic plant

SOLAR 1.1: DEVELOPMENT OF SOFTWARE FOR SELECTING COMMERCIALLY AVAILABLE PHOTOVOLTAIC PANELS, INCLUDING THE ECONOMIC ANALYSIS

Photovoltaic energy represents an opportunity to produce electricity in a clean manner. It can be applied in all world places, in particular in the developing countries, where there are places where electricity grids are unreliable or non-existent and is inconvenient to make investments in a grids expansion. In remote locations photovoltaic power supplies often the most economic and cleaner option to produce electric energy. In addition, many developing countries have high radiation levels year round because of their latitude. The software SOLAR 1.1 was developed with purpose of helping the choice of photovoltaic panels available commercially including electric needs calculation for the installation. This new version of program also help to conduce the economic analysis for grid connected or stand alone photovoltaic systems for the choice of convenient values of interest rate and payback period. In this version of the software is possible to select the language among English, Italian and Portuguese. The software choices the panels in its archive that contains more of 250 types of photovoltaic modules made by 35 producers. The selection provides as output three modules, the cheapest for each cell type: monocrystalline, multicrystalline and amorphous. The software archive can be updated adding new item or editing the inserted items. The economic analysis can be operated by SOLAR 1.1 in each of the chosen panels. This analysis gives as output all the values of the costs in the photovoltaic system and the diagrams with the electricity cost and the expected annual saving trend with variation of the amortisation period and for different values of the interest rate and the governmental subsidy rate

Unleashing the Potential of LTE for Next Generation Railway Communications

In an increasingly demanding marketplace that will put great strain on railway services, research on broadband wireless communication must continue to strive for improvement. Based on the mature narrowband GSM technology, Global System for Mobile Communications-Railways (GSM-R) has been deployed both for operational and voice communications. Although GSM-R fulfills the requirements of current railway services, it imposes limited capacity and high costs that restrict enhancements of operational efficiency, passenger security and transport quality. 4G Long Term Evolution (LTE) is expected to be the natural successor of GSM-R not only for its technical advantages and increasing performance, but also due to the current evolution of general-purpose communication systems. This paper examines the key features of LTE as well as its technical ability to support both the migration of current railway services and the provisioning of future ones.Comment: This is a portion of the ACCEPTED VERSION of the published document in: Kassab, M., Berbineau,M., Vinel, A., Jonsson, M., Garcia, F., Soler, J. (eds) Communication Technologies for Vehicles. Nets4Cars/Nets4Trains/Nets4Aircraft 2015. Lecture Notes in Computer Science, vol 9066. Springer, Cham. https://doi.org/10.1007/978-3-319-17765-6_1

BRS Aroeira - Nova cultivar de algodoeiro para Mato Grosso do Sul.

bitstream/item/24861/1/COT200255.pdfDocumento on-line

Cultivares, densidades e espaçamentos entre fileiras na cultura do algodoeiro em Mato Grosso do Sul.

Este trabalho teve como objetivo avaliar o comportamento de quatro cultivares de algodoeiro em três locais do Estado de Mato Grosso do Sul, utilizando-se espaçamentos entre fileiras de 0,30; 0,60; 0,90 e 1,20 m, nas densidades de 4, 8, 12 e 16 plantas m-1.bitstream/item/38777/1/BP200523.pd

Using step width to compare locomotor biomechanics between extinct, non-avian theropod dinosaurs and modern obligate bipeds

How extinct, non-avian theropod dinosaurs locomoted is a subject of considerable interest, as is the manner in which it evolved on the line leading to birds. Fossil footprints provide the most direct evidence for answering these questions. In this study, step width—the mediolateral (transverse) distance between successive footfalls—was investigated with respect to speed (stride length) in non-avian theropod trackways of Late Triassic age. Comparable kinematic data were also collected for humans and 11 species of ground-dwelling birds. Permutation tests of the slope on a plot of step width against stride length showed that step width decreased continuously with increasing speed in the extinct theropods (p < 0.001), as well as the five tallest bird species studied (p < 0.01). Humans, by contrast, showed an abrupt decrease in step width at the walk–run transition. In the modern bipeds, these patterns reflect the use of either a discontinuous locomotor repertoire, characterized by distinct gaits (humans), or a continuous locomotor repertoire, where walking smoothly transitions into running (birds). The non-avian theropods are consequently inferred to have had a continuous locomotor repertoire, possibly including grounded running. Thus, features that characterize avian terrestrial locomotion had begun to evolve early in theropod history

Efeito protetor ("savener") de inseticidas contra a fitotoxicidade causada pelo herbicida clomazone no algodoeiro.

bitstream/item/65615/1/Cot30-2000.pd

SOLAR SOFTWARE APPLIED TO DESIGN A PHOTOVOLTAIC SYSTEM TO SUPPLY THE ENERGY DEMAND OF AN ITALIAN SCHOOL

This paper has as objective to describe the use of SOLAR 1.1 software todesign a system for supplying a part of the electric demand of a schoolsituated in Umbertide, comparing the use o SOLAR 1.1 to real results of asystem implanted yet. This software version helps also to conduce theeconomic analysis for grid connected or standalone photovoltaic systemsfor the choice of convenient values of investment rate and annuity factorand it calculates the payback period of investment in the photovoltaic plant