587 research outputs found

    Dinámica de aguas superficiales de tres períodos continuos de Landsat; diferencias subregionales en llanuras argentinas

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    [EN] The Pampean region in Argentina is an extensive plain characterized by abundant shallow lakes that fulfill many environmental, ecological, and social functions. This study aims to detect the multiannual lake area changes in this region during 2001-2009 using remote sensing, including lakes as small as ≥10,000 m2 or 1 ha. Landsat scenes of the wet (2008-2009), normal (2006), and dry (2008-2009) seasons were obtained, and using remote sensing techniques, the number and area of shallow lakes were calculated. The spatiotemporal variation of shallow lakes was studied in different climate periods in eight singular subregions. Spatial associations between annual precipitation and lake number and area were analyzed through the development of a Geographic Information System (GIS) at a subregional scale. During the study period the total lake area in the Pampean region decreased by 5257.39 km2 (62 %), but each subregion showed different responses to climatic events. In seven of them, the differences between climate periods prove to be statistically significant (P>0.01). The relationship between precipitation and lake number and area revealed the domain of positive association. We conclude that climate factors play a dominant role in lake changes across the Pampean plains. However, other factors such as origin, topographic and edaphic characteristics intensify or mitigate changes in surface hydrology.[ES] La Región Pampeana en Argentina es una extensa planicie caracterizada por abundantes lagunas que cumplen numerosas funciones ambientales, ecológicas y sociales. Este estudio tiene como objetivo detectar los cambios plurianuales del área lagunar en esta región durante el período 2001-2009 utilizando la teledetección, incluidos lagos tan pequeños como ≥ 10.000 m2 o 1 ha. Se obtuvieron escenas Landsat de las estaciones húmeda (2008-2009), normal (2006) y seca (2008-2009) y, mediante técnicas de teledetección, se calculó el número y el área de las lagunas. Se estudió su variación espacio-temporal en diferentes períodos climáticos en ocho subregiones singulares. Se analizaron las correlaciones espaciales entre la precipitación anual y el número y el área de los lagos mediante el desarrollo de un Sistema de Información Geográfica (SIG). Durante el período de estudio el área total de lagos en la región pampeana disminuyó en 5.257,39  km2 (62 %), pero cada subregión mostró diferentes respuestas a los eventos climáticos. En siete de ellos, las diferencias entre periodos climáticos resultan estadísticamente significativas (P>0,01). La relación entre la precipitación con el número y área de las lagunas reveló el dominio de asociaciones positivas. Si bien el clima juega un papel dominante en los cambios en las lagunas de planicie, otros factores, como el origen, las características topográficas y edáficas, intensifican o mitigan los cambios en la hidrología superficial.Authors would like to thank the Consejo Nacional de Investigaciones Científicas y Técnicas for supporting this study. Besides, to the United States Geological Survey for supplying the information analyzed in this study. This work was carried out with the aid of a grant from the Inter-American Institute for Global Change Research (IAI) CRN3038, which is supported by the US National Science Foundation (Grant GEO-1128040)Aliaga, VS.; Piccolo, M.; Perillo, G. (2021). Surface water extent dynamics from three periods of continuous Landsat time series; subregional differences across Argentine plains. Revista de Teledetección. 0(58):131-145. http://hdl.handle.net/10251/169769OJS13114505

    Polaron Transport in the Paramagnetic Phase of Electron-Doped Manganites

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    The electrical resistivity, Hall coefficient, and thermopower as functions of temperature are reported for lightly electron-doped Ca(1-x)La(x)MnO(3)(0 <= x <= 0.10). Unlike the case of hole-doped ferromagnetic manganites, the magnitude and temperature dependence of the Hall mobility for these compounds is found to be inconsistent with small-polaron theory. The transport data are better described by the Feynman polaron theory and imply intermediate coupling (alpha \~ 5.4) with a band effective mass, m*~4.3 m_0, and a polaron mass, m_p ~ 10 m_0.Comment: 7 pp., 7 Fig.s, to be published, PR

    Squeezed States of the Generalized Minimum Uncertainty State for the Caldirola-Kanai Hamiltonian

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    We show that the ground state of the well-known pseudo-stationary states for the Caldirola-Kanai Hamiltonian is a generalized minimum uncertainty state, which has the minimum allowed uncertainty ΔqΔp=σ0/2\Delta q \Delta p = \hbar \sigma_0/2, where σ0(1)\sigma_0 (\geq 1) is a constant depending on the damping factor and natural frequency. The most general symmetric Gaussian states are obtained as the one-parameter squeezed states of the pseudo-stationary ground state. It is further shown that the coherent states of the pseudo-stationary ground state constitute another class of the generalized minimum uncertainty states.Comment: RevTex4, 9 pages, no fingure; to be published in Journal of Physics

    A-site Randomness Effect on Structural and Physical Properties of Ba-based Perovskite Manganites

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    The discovery of novel structural and physical properties in the AA-site ordered manganite RRBaMn2_{2}O6_{6} (RR = Y and rare earth elements) has demanded new comprehension about perovskite manganese oxides. In the present study, the AA-site disordered form, R0.5R_{0.5}Ba0.5_{0.5}MnO3_{3}, has been investigated and compared with both RRBaMn2_{2}O6_{6} and R0.5A0.5R_{0.5}A_{0.5}MnO3_{3} (AA: Sr, Ca) in the structures and electromagnetic properties. R0.5R_{0.5}Ba0.5_{0.5}MnO3_{3} has a primitive cubic perovskite cell in the structure and magnetic glassy states are dominant as its ground state, in contrast to the ordinary disordered R0.5A0.5R_{0.5}A_{0.5}MnO3_{3} (AA: Sr, Ca). In Pr-compounds with various degrees of Pr/Ba randomness at the AA-sites, the AA-site disorder gradually suppresses both ferromagnetic and A-type antiferromagnetic transitions and finally leads to a magnetic glassy state in Pr0.5_{0.5}Ba0.5_{0.5}MnO3_{3}. A peculiar behavior, multi-step magnetization and resistivity change, has been observed in Pr0.5_{0.5}Ba0.5_{0.5}MnO3_{3}. These properties could be closely related to any spatial heterogeneity caused by the random distribution of Ba2+^{2 +} and R3+R^{3 +} with much different ionic radius.Comment: 9 pages, to be published in J. Phys. Soc. Jpn. 73 Aug. (2004

    Charge and spin inhomogeneous phases in the Ferromagnetic Kondo Lattice Model

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    We study numerically the one-dimensional ferromagnetic Kondo lattice. This model is widely used to describe nickel and manganese perovskites. Due to the competition between double and super-exchange, we find a region where the formation of magnetic polarons induces a charge-ordered state. This ordering is present even in the absence of any inter-site Coulomb repulsion. There is an insulating gap associated to the charge structure formation. We also study the insulator-metal transition induced by a magnetic field which removes simultaneously both charge and spin ordering.Comment: 7 pages, 11 figure

    Evaluation of the spectroscopic performance of the integrated multi-channel charge-sensitive preamplifier of TRACE with a silicon detector prototype

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    In this work the experimental results are presented showing the spectroscopic performance of the ASIC multichannel charge-sensitive preamplifier of TRACE (TRacking Array for light Charged particle Ejectiles). The results were obtained connecting a silicon pad detector to a custom-designed preamplifier board with eight ASIC CSPs. The detector and the board were put in a vacuum chamber with a triple Am-Cm-Pu alpha source. The output signals were digitized with four FPGApowered 100 MHz 14-bit resolution digitizer cards. The energy resolution obtained is around 22 keV at 5486 keV. The results are very encouraging and pave the way for future developments

    The nanoscale phase separation in hole-doped manganites

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    A macroscopic phase separation, in which ferromagnetic clusters are observed in an insulating matrix, is sometimes observed, and believed to be essential to the colossal magnetoresistive (CMR) properties of manganese oxides. The application of a magnetic field may indeed trigger large magnetoresistance effects due to the percolation between clusters allowing the movement of the charge carriers. However, this macroscopic phase separation is mainly related to extrinsic defects or impurities, which hinder the long-ranged charge-orbital order of the system. We show in the present article that rather than the macroscopic phase separation, an homogeneous short-ranged charge-orbital order accompanied by a spin glass state occurs, as an intrinsic result of the uniformity of the random potential perturbation induced by the solid solution of the cations on the AA-sites of the structure of these materials. Hence the phase separation does occur, but in a more subtle and interesting nanoscopic form, here referred as ``homogeneous''. Remarkably, this ``nanoscale phase separation'' alone is able to bring forth the colossal magnetoresistance in the perovskite manganites, and is potentially relevant to a wide variety of other magnetic and/or electrical properties of manganites, as well as many other transition metal oxides, in bulk or thin film form as we exemplify throughout the article.Comment: jpsj2 TeX style (J. Phys. Soc. Jpn); 18 pages, 7 figure
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