Impacto do aumento da concentração de CO2 atmosférico sobre a microbiota do solo rizosférico de arroz.

A intensificação da atividade antrópica está causando significativo aumento da concentração de dióxido de carbono (CO2) na atmosfera, resultando em alterações no clima do planeta que devem ser acentuadas nas próximas décadas. Além das mudanças climáticas previstas, impactos também ocorrerão no ambiente biótico. O trabalho teve por objetivo avaliar os efeitos do aumento do CO2 atmosférico na microbiota do solo rizosférico de arroz (cultivar Agulha Precoce), em ensaio conduzido em estufas de topo aberto. Os tratamentos com injeção automatizada do gás apresentaram concentração média de 613 ppm de CO2. Como testemunha, foram utilizadas parcelas sem estufa e sem injeção do gás. Não houve efeito dos tratamentos no carbono da biomassa microbiana, na hidrólise de diacetato de fluoresceína, no desprendimento de CO2 e na condutividade elétrica do solo rizosférico e no número de bactérias diazotróficas endofíticas isoladas das raízes utilizando-se meio de cultura JNFb semi-específico para Herbaspirillum. Os tratamentos com estufa apresentaram aumento do pH do solo, sendo que o maior aumento foi obtido no tratamento com injeção de CO2

Strong low-frequency quantum correlations from a four-wave mixing amplifier

We show that a simple scheme based on nondegenerate four-wave mixing in a hot atomic vapor behaves like a near-perfect phase-insensitive optical amplifier, which can generate bright twin beams with a measured quantum noise reduction in the intensity difference of more than 8 dB, close to the best optical parametric amplifiers and oscillators. The absence of a cavity makes the system immune to external perturbations, and the strong quantum noise reduction is observed over a large frequency range.Comment: 4 pages, 4 figures. Major rewrite of the previous version. New experimental results and further analysi

Gravitational Waveguides in Cosmology

We discuss the possibility that, besides the usual gravitational lensing, there may exist a sort of gravitational waveguiding in cosmology which could explain some anomalous phenomena which cannot be understood by the current gravitational lensing models as the existence of "brothers" objects having different brilliancy but similar spectra and redshifts posed on the sky with large angular distance. Furthermore, such a phenomena could explain the huge luminosities coming from quasars using the cosmological structures as selfoc-type or planar waveguide. We describe the gravitational waveguide theory and then we discuss possible realizations in cosmology.Comment: 14 pages, latex, submitted to Int. Jou. Mod. Phys.

VEGAS: a VST Early-type GAlaxy Survey. IV. NGC 1533, IC 2038 and IC 2039: an interacting triplet in the Dorado group

This paper focuses on NGC 1533 and the pair IC 2038 and IC 2039 in Dorado a nearby, clumpy, still un-virialized group. We obtained their surface photometry from deep OmegaCAM@ESO-VST images in g and r bands. For NGC 1533, we map the surface brightness down to $\mu_g \simeq 30.11$ mag/arcsec$^{2}$ and $\mu_r \simeq 28.87$ mag/arcsec$^{2}$ and out to about $4R_e$. At such faint levels the structure of NGC 1533 appear amazingly disturbed with clear structural asymmetry between inner and outer isophotes in the North-East direction. We detect new spiral arm-like tails in the outskirts, which might likely be the signature of a past interaction/merging event. Similarly, IC 2038 and IC 2039 show tails and distortions indicative of their ongoing interaction. Taking advantages of deep images, we are able to detect the optical counterpart to the HI gas. The analysis of the new deep data suggests that NGC 1533 had a complex history made of several interactions with low-mass satellites that generated the star-forming spiral-like structure in the inner regions and are shaping the stellar envelope. In addition, the VST observations show that also the two less luminous galaxies, IC 2038 and IC 2039, are probably interacting each-other and, in the past, IC 2038 could have also interacted with NGC 1533, which stripped away gas and stars from its outskirts. The new picture emerging from this study is of an interacting triplet, where the brightest galaxy NGC 1533 has ongoing mass assembly in the outskirts.Comment: Accepted for publication in The Astronomical Journal. High-resolution version of paper is available at the following link: https://www.dropbox.com/preview/VEGAS_IV.pdf?role=persona

Charge pairing, superconducting transition and supersymmetry in high-temperature cuprate superconductors

We propose a model for high-T$_{c}$ superconductors, valid for $0\leq\delta\leq\delta_{SC}$, that includes both the spin fluctuations of the Cu$^{++}$ magnetic ions and of the O$^{--}$ doped holes. Spin-charge separation is taken into account with the charge of the doped holes being associated to quantum skyrmion excitations (holons) of the Cu$^{++}$ spin background. The holon effective interaction potential is evaluated as a function of doping, indicating that Cooper pair formation is determined by the competition between the spin fluctuations of the Cu$^{++}$ background and of spins of the O$^{--}$ doped holes (spinons). The superconducting transition occurs when the spinon fluctuations dominate, thereby reversing the sign of the interaction. At this point ($\delta = \delta_{SC}$), the theory is supersymmetric at short distances and, as a consequence, the leading order results are not modified by radiative corrections. The critical doping parameter for the onset of superconductivity at T=0 is obtained and found to be a universal constant determined by the shape of the Fermi surface. Our theoretical values for $\delta_{SC}$ are in good agreement with the experiment for both LSCO and YBCO.Comment: RevTex, 4 pages, no figure

A matrix model for the topological string II: The spectral curve and mirror geometry

In a previous paper, we presented a matrix model reproducing the topological string partition function on an arbitrary given toric Calabi-Yau manifold. Here, we study the spectral curve of our matrix model and thus derive, upon imposing certain minimality assumptions on the spectral curve, the large volume limit of the BKMP "remodeling the B-model" conjecture, the claim that Gromov-Witten invariants of any toric Calabi-Yau 3-fold coincide with the spectral invariants of its mirror curve.Comment: 1+37 page

Branes as Stable Holomorphic Line Bundles On the Non-Commutative Torus

It was recently suggested by A. Kapustin that turning on a $B$-field, and allowing some discrepancy between the left and and right-moving complex structures, must induce an identification of B-branes with holomorphic line bundles on a non-commutative complex torus. We translate the stability condition for the branes into this language and identify the stable topological branes with previously proposed non-commutative instanton equations. This involves certain topological identities whose derivation has become familiar in non-commutative field theory. It is crucial for these identities that the instantons are localized. We therefore explore the case of non-constant field strength, whose non-linearities are dealt with thanks to the rank-one Seiberg--Witten map.Comment: 12 pages, LaTe