Sistemas agroflorestais: restauração ambiental e produção no âmbito da Floresta Ombrófila Mista.

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Near-infrared spatially resolved spectroscopy of (136108) Haumea's multiple system

The transneptunian region of the solar system is populated by a wide variety of icy bodies showing great diversity. The dwarf planet (136108) Haumea is among the largest TNOs and displays a highly elongated shape and hosts two moons, covered with crystalline water ice like Hamuea. Haumea is also the largest member of the sole TNO family known to date. A catastrophic collision is likely responsible for its unique characteristics. We report here on the analysis of a new set of observations of Haumea obtained with SINFONI at the ESO VLT. Combined with previous data, and using light-curve measurements in the optical and far infrared, we carry out a rotationally resolved spectroscopic study of the surface of Haumea. We describe the physical characteristics of the crystalline water ice present on the surface of Haumea for both regions, in and out of the Dark Red Spot (DRS), and analyze the differences obtained for each individual spectrum. The presence of crystalline water ice is confirmed over more than half of the surface of Haumea. Our measurements of the average spectral slope confirm the redder characteristic of the spot region. Detailed analysis of the crystalline water-ice absorption bands do not show significant differences between the DRS and the remaining part of the surface. We also present the results of applying Hapke modeling to our data set. The best spectral fit is obtained with a mixture of crystalline water ice (grain sizes smaller than 60 micron) with a few percent of amorphous carbon. Improvements to the fit are obtained by adding ~10% of amorphous water ice. Additionally, we used the IFU-reconstructed images to measure the relative astrometric position of the largest satellite Hi`iaka and determine its orbital elements. An orbital solution was computed with our genetic-based algorithm GENOID and our results are in full agreement with recent results.Comment: Accepted for publication in A&

The formation of the solar system

The solar system started to form about 4.56 Gyr ago and despite the long intervening time span, there still exist several clues about its formation. The three major sources for this information are meteorites, the present solar system structure and the planet-forming systems around young stars. In this introduction we give an overview of the current understanding of the solar system formation from all these different research fields. This includes the question of the lifetime of the solar protoplanetary disc, the different stages of planet formation, their duration, and their relative importance. We consider whether meteorite evidence and observations of protoplanetary discs point in the same direction. This will tell us whether our solar system had a typical formation history or an exceptional one. There are also many indications that the solar system formed as part of a star cluster. Here we examine the types of cluster the Sun could have formed in, especially whether its stellar density was at any stage high enough to influence the properties of today's solar system. The likelihood of identifying siblings of the Sun is discussed. Finally, the possible dynamical evolution of the solar system since its formation and its future are considered.Comment: 36 pages, 7 figures, invited review in Physica Script

Bamboo influence on natural regeneration - a case study in a Araucaria Forest fragment in Brazil.

IUFROLAT 2013. Disponibilizado online. Resumen

Spin - Phonon Coupling in Nickel Oxide Determined from Ultraviolet Raman Spectroscopy

Nickel oxide (NiO) has been studied extensively for various applications ranging from electrochemistry to solar cells [1,2]. In recent years, NiO attracted much attention as an antiferromagnetic (AF) insulator material for spintronic devices [3-10]. Understanding the spin - phonon coupling in NiO is a key to its functionalization, and enabling AF spintronics' promise of ultra-high-speed and low-power dissipation [11,12]. However, despite its status as an exemplary AF insulator and a benchmark material for the study of correlated electron systems, little is known about the spin - phonon interaction, and the associated energy dissipation channel, in NiO. In addition, there is a long-standing controversy over the large discrepancies between the experimental and theoretical values for the electron, phonon, and magnon energies in NiO [13-23]. This gap in knowledge is explained by NiO optical selection rules, high Neel temperature and dominance of the magnon band in the visible Raman spectrum, which precludes a conventional approach for investigating such interaction. Here we show that by using ultraviolet (UV) Raman spectroscopy one can extract the spin - phonon coupling coefficients in NiO. We established that unlike in other materials, the spins of Ni atoms interact more strongly with the longitudinal optical (LO) phonons than with the transverse optical (TO) phonons, and produce opposite effects on the phonon energies. The peculiarities of the spin - phonon coupling are consistent with the trends given by density functional theory calculations. The obtained results shed light on the nature of the spin - phonon coupling in AF insulators and may help in developing innovative spintronic devices.Comment: 16 pages; 2 figure

Avaliação do comportamento da regeneração natural em duas subtipologias de Floresta Ombrófila Mista.

Resumo

Bose-Einstein Condensation of S = 1 Ni spin degrees of freedom in NiCl2-4SC(NH2)2

It has recently been suggested that the organic compound NiCl$_2$-4SC(NH$_2$)$_2$ (DTN) exhibits Bose-Einstein Condensation (BEC) of the Ni spin degrees of freedom for fields applied along the tetragonal c-axis. The Ni spins exhibit 3D XY-type antiferromagnetic order above a field-induced quantum critical point at $H_{c1} \sim 2$ T. The Ni spin fluid can be characterized as a system of effective bosons with a hard-core repulsive interaction in which the antiferromagnetic state corresponds to a Bose-Einstein condensate (BEC) of the phase coherent $S = 1$ Ni spin system. We have investigated the the high-field phase diagram and the occurrence of BEC in DTN by means of specific heat and magnetocaloric effect measurements to dilution refrigerator temperatures. Our results indicate that a key prediction of BEC is satisfied; the magnetic field-temperature quantum phase transition line $H_c(T)-H_{c1} \propto T^\alpha$ approaches a power-law at low temperatures, with an exponent $\alpha = 1.47 \pm 0.06$ at the quantum critical point, consistent with the BEC theory prediction of $\alpha = 1.5$.Comment: 4 pages, 4 figure

Estimativa da energia cultural na cotonicultura arbórea no Nordeste brasileiro, comparando-se o Mocó tradicional com o precoce.

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