The whole mesh Deformation Model for 2D and 3D image segmentation

In this paper we present a novel approach for image segmentation using Active Nets and Active Volumes. Those solutions are based on the Deformable Models, with slight difference in the method for describing the shapes of interests - instead of using a contour or a surface they represented the segmented objects with a mesh structure, which allows to describe not only the surface of the objects but also to model their interiors. This is obtained by dividing the nodes of the mesh in two categories, namely internal and external ones, which will be responsible for two different tasks. In our new approach we propose to negate this separation and use only one type of nodes. Using that assumption we manage to significantly shorten the time of segmentation while maintaining its quality

Quantificação e isolamento de bactérias diazotróficas associadas a coqueiro (Cocos nucifera L.).

bitstream/item/87943/1/CPATC-PESQ.-AND.-23-97.pd

Emergent magnetic degeneracy in iron pnictides due to the interplay between spin-orbit coupling and quantum fluctuations

Recent experiments in iron pnictide superconductors reveal that, as the putative magnetic quantum critical point is approached, different types of magnetic order coexist over a narrow region of the phase diagram. Although these magnetic configurations share the same wave-vectors, they break distinct symmetries of the lattice. Importantly, the highest superconducting transition temperature takes place close to this proliferation of near-degenerate magnetic states. In this paper, we employ a renormalization group calculation to show that such a behavior naturally arises due to the effects of spin-orbit coupling on the quantum magnetic fluctuations. Formally, the enhanced magnetic degeneracy near the quantum critical point is manifested as a stable Gaussian fixed point with a large basin of attraction. Implications of our findings to the superconductivity of the iron pnictides are also discussed.Comment: 6 pages, 2 figures, published versio

Magnetic phase diagram of the iron pnictides in the presence of spin-orbit coupling: Frustration between C2C_2 and C4C_4 magnetic phases

We investigate the impact of spin anisotropic interactions, promoted by spin-orbit coupling, on the magnetic phase diagram of the iron-based superconductors. Three distinct magnetic phases with Bragg peaks at $(\pi,0)$ and $(0,\pi)$ are possible in these systems: one $C_2$ (i.e. orthorhombic) symmetric stripe magnetic phase and two $C_4$ (i.e. tetragonal) symmetric magnetic phases. While the spin anisotropic interactions allow the magnetic moments to point in any direction in the $C_2$ phase, they restrict the possible moment orientations in the $C_4$ phases. As a result, an interesting scenario arises in which the spin anisotropic interactions favor a $C_2$ phase, but the other spin isotropic interactions favor a $C_4$ phase. We study this frustration via both mean-field and renormalization-group approaches. We find that, to lift this frustration, a rich magnetic landscape emerges well below the magnetic transition temperature, with novel $C_2$, $C_4$, and mixed $C_2$-$C_4$ phases. Near the putative magnetic quantum critical point, spin anisotropies promote a stable Gaussian fixed point in the renormalization-group flow, which is absent in the spin isotropic case, and is associated with a near-degeneracy between $C_2$ and $C_4$ phases. We argue that this frustration is the reason why most $C_4$ phases in the iron pnictides only appear inside the $C_2$ phase, and discuss additional manifestations of this frustration in the phase diagrams of these materials.Comment: 21 pages, 19 figures, published versio

Enhanced nematic fluctuations near an antiferromagnetic Mott insulator and possible application to high-TcT_{c} cuprates

Motivated by the widespread experimental observations of nematicity in strongly underdoped cuprate superconductors, we investigate the possibility of enhanced nematic fluctuations in the vicinity of a Mott insulator that displays N\'eel-type antiferromagnetic order. By performing a strong-coupling expansion of an effective model that contains both Cu-$d$ and O-$p$ orbitals on the square lattice, we demonstrate that quadrupolar fluctuations in the $p$-orbitals inevitably generate a biquadratic coupling between the spins of the $d$-orbitals. The key point revealed by our classical Monte Carlo simulations and large-$N$ calculations is that the biquadratic term favors local stripe-like magnetic fluctuations, which result in an enhanced nematic susceptibility that onsets at a temperature scale determined by the effective Heisenberg exchange $J$. We discuss the impact of this type of nematic order on the magnetic spectrum and outline possible implications on our understanding of nematicity in the cuprates.Comment: 11 pages, 4 figures; includes Supplemental Material (14 pages, 4 figures

Seleção de rizóbios nativos para guandu, caupi e feijão-de-porco nos tabuleiros costeiros de Sergipe.

A inoculação de estirpes de rizóbios em sementes de feijão-de-porco (Canavalia ensiformis), caupi (Vigna unguiculata) e guandu (Cajanus cajan), recomendadas para outras regiões do País, não tem resultado em incrementos nas taxas de fixação biológica de N2 nem no crescimento dessas leguminosas em solos dos tabuleiros costeiros de Sergipe. Os objetivos deste trabalho foram avaliar a eficiência simbiótica de rizóbios nativos dos tabuleiros costeiros associados a essas leguminosas e a tolerância deles a estresses. Das 17 estirpes de rizóbios isoladas e analisadas em casa de vegetação, quatro foram selecionadas para o guandu, sete para o caupi e três para o feijão-de-porco. O número e a massa de nódulos secos por planta correlacionaram-se com a massa da parte aérea seca, a área foliar e o N total acumulado nas folhas das três leguminosas. Os mesmos rizóbios foram eficientes para o caupi e para o guandu. Três estirpes do guandu (R35, R43 e R45) e duas do caupi (R10 e R17) foram caracterizadas in vitro e todas apresentaram tolerância às concentrações elevadas de ácido nalidíxico, cloranfenicol e tetraciclina, porém, foram sensíveis à estreptomicina e à kanamicina. Todas as estirpes cresceram a 35ºC e, exceto a R17, toleraram o alumínio (10 mg L-1)

Caracterização genética de rizóbios nativos dos tabuleiros costeiros eficientes em culturas do guandu e caupi.

O objetivo deste trabalho foi caracterizar geneticamente sete estirpes de rizóbios nativos dos tabuleiros costeiros de Sergipe com alta eficiência de fixação biológica do N2 em associação com guandu (Cajanus cajan) e caupi (Vigna unguiculata). A amplificação do DNA pela técnica de PCR (polymerase chain reaction) com o oligonucleotídeo específico BOX indicou um grau elevado de diversidade genética, uma vez que todas as estirpes apresentaram perfis únicos de DNA. A análise por BOX-PCR revelou, ainda, que essa metodologia é eficiente para diferenciar estirpes, mas não para a diferenciação de espécies de rizóbio. Pela técnica do RFLP (restriction fragment length polymorphism) da região do DNA que codifica o gene 16S rRNA e da região intergênica entre os genes 16S e 23S rRNA, com cinco enzimas de restrição, bem como pelo seqüenciamento parcial da região do 16S rRNA, foi possível classificar as estirpes nos gêneros Bradyrhizobium e Rhizobium. Houve coerência entre as análises envolvendo a região do 16S rRNA, mas o agrupamento com uma das estirpes diferiu pela análise do espaço intergênico. Os resultados obtidos com a estirpe R11 indicam variabilidade genética elevada em relação às espécies de rizóbios descritas, inclusive diferindo em diversas bases da região do 16S rRNA, e podem indicar uma nova espécie

Two-band superconductivity in doped SrTiO3_{3} films and interfaces

We investigate the possibility of multi-band superconductivity in SrTiO$_{3}$ films and interfaces using a two-dimensional two-band model. In the undoped compound, one of the bands is occupied whereas the other is empty. As the chemical potential shifts due to doping by negative charge carriers or application of an electric field, the second band becomes occupied, giving rise to a strong enhancement of the transition temperature and a sharp feature in the gap functions, which is manifested in the local density of states spectrum. By comparing our results with tunneling experiments in Nb-doped SrTiO$_{3}$, we find that intra-band pairing dominates over inter-band pairing, unlike other known multi-band superconductors. Given the similarities with the value of the transition temperature and with the band structure of LaAlO$_{3}$/SrTiO$_{3}$ heterostructures, we speculate that the superconductivity observed in SrTiO$_{3}$ interfaces may be similar in nature to that of bulk SrTiO$_{3}$, involving multiple bands with distinct electronic occupations.Comment: revised expanded versio