Euclidean thermal spinor Green's function in the spacetime of a straight cosmic string

Within the framework of the quantum field theory at finite temperature on a conical space, we determine the Euclidean thermal spinor Green's function for a massless spinor field. We then calculate the thermal average of the energy-momentum tensor of a thermal bath of massless fermions. In the high-temperature limit, we find that the straight cosmic string does not perturb the thermal bathComment: 11 pages, latex, no figure

Fast pick up technique for high quality heterostructures of bilayer graphene and hexagonal boron nitride

We present a fast method to fabricate high quality heterostructure devices by picking up crystals of arbitrary sizes. Bilayer graphene is encapsulated with hexagonal boron nitride to demonstrate this approach, showing good electronic quality with mobilities ranging from 17 000 cm^2/V/s at room temperature to 49 000 cm^2/V/s at 4.2 K, and entering the quantum Hall regime below 0.5 T. This method provides a strong and useful tool for the fabrication of future high quality layered crystal devices.Comment: 5 pages, 3 figure

Cosmic String in Scalar-Tensor Gravity

The gravitational properties of a local cosmic string in the framework of scalar-tensor gravity are examined. We find the metric in the weak-field approximation and we show that, contrary to the General Relativity case, the cosmic string in scalar-tensor gravitation exerces a force on non-relativistic, neutral test particle. This force is proportional to the derivative of the conformal factor $A^{2}(\phi)$ and it is always attractive. Moreover, this force could have played an important role at the Early Universe, although nowadays it can be neglegible. It is also shown that the angular separation $\delta\varphi$ remains unaltered for scalar-tensor cosmic strings.Comment: 15 pages, LATEX, no figure

Controlling spin relaxation in hexagonal BN-encapsulated graphene with a transverse electric field

We experimentally study the electronic spin transport in hBN encapsulated single layer graphene nonlocal spin valves. The use of top and bottom gates allows us to control the carrier density and the electric field independently. The spin relaxation times in our devices range up to 2 ns with spin relaxation lengths exceeding 12 $\mu$m even at room temperature. We obtain that the ratio of the spin relaxation time for spins pointing out-of-plane to spins in-plane is $\tau_{\bot} / \tau_{||} \approx$ 0.75 for zero applied perpendicular electric field. By tuning the electric field this anisotropy changes to $\approx$0.65 at 0.7 V/nm, in agreement with an electric field tunable in-plane Rashba spin-orbit coupling

Vacuum Polarization at Finite Temperature around a Magnetic Flux Cosmic String

We consider a general situation where a charged massive scalar field $\phi(x)$ at finite temperature interacts with a magnetic flux cosmic string. We determine a general expression for the Euclidean thermal Green's function of the massive scalar field and a handy expression for a massless scalar field. With this result, we evaluate the thermal average $$ and the thermal average of the energy-momentum tensor of a nonconformal massless scalar field.Comment: 22 pages, latex, no figure

Teores de nitrogênio e de clorofilas em folhas de feijão e de soja inoculados com rizóbios.

Com o objetivo de avaliar os teores de nitrogênio total e de clorofila total em plantas de feijão e de soja conduziu-se um experimento em Goiânia-GO, utilizando delineamento inteiramente casualizado com três repetições

Visual Binaries in the Orion Nebula Cluster

We have carried out a major survey for visual binaries towards the Orion Nebula Cluster using HST images obtained with an H-alpha filter. Among 781 likely ONC members more than 60" from theta-1 Ori C, we find 78 multiple systems (75 binaries and 3 triples), of which 55 are new discoveries, in the range from 0.1" to 1.5". About 9 binaries are likely line-of-sight associations. We find a binary fraction of 8.8%+-1.1% within the limited separation range from 67.5 to 675 AU. The field binary fraction in the same range is a factor 1.5 higher. Within the range 150 AU to 675 AU we find that T Tauri associations have a factor 2.2 more binaries than the ONC. The binary separation distribution function of the ONC shows unusual structure, with a sudden steep decrease in the number of binaries as the separation increases beyond 0.5", corresponding to 225 AU. We have measured the ratio of binaries wider than 0.5" to binaries closer than 0.5" as a function of distance from the Trapezium, and find that this ratio is significantly depressed in the inner region of the ONC. The deficit of wide binaries in the central part of the cluster is likely due to dissolution or orbital change during their passage through the potential well of the inner cluster region. Many of the companions are likely to be brown dwarfs.Comment: 27 pages, 10 figures, 2 tables, accepted by the Astronomical Journa

Efeito de substratos na produção de porta-enxertos de bacurizeiro (Platonia insignis Mart.).

O bacurizeiro é uma espécie frutífera nativa da Amazônia, com provável centro de origem no estado do Pará. A produção de mudas de bacurizeiro por sementes não é aconselhável pois apresenta longo período juvenil. Assim, a propagação por sementes só é recomendada para produção de porta-enxertos. O objetivo deste trabalho foi avaliar os efeitos de substratos e adubação na formação de porta-enxertos de bacurizeiro

Avaliação de tipos de recipientes na formação de porta-enxertos de bacuri (Platonia insignis Mart.).

O objetivo deste trabalho foi avaliar o efeito de diferentes tipos de recipientes na formação de porta-enxertos de bacurizeiro. Foram avaliados os recipientes: saco de polietileno preto de 18 x 35 cm (controle), citrivaso, citritubo, tubete PET-2,5 L, tubete PET-1,5 L e tubete 0,8 L. Em todos os recipientes, exceto o controle, utilizou-se substrato composto de terra vegetal, casca de arroz carbonizada e plantmax® na proporção de 3:5:2 e enriquecido com 1,5 kg de superfosfato simples/m-3 de substrato. Foram avaliadas as seguintes características: diâmetro da raiz primária no dia do corte, número de dias após o corte para início da brotação, percentagem de brotação da raiz primária e diâmetro de caule aos 150 dias após o corte. Aos 240 dias após a brotação avaliaram-se ainda: diâmetro de caule, diâmetro da raiz, pesos frescos da parte aérea e das raízes, e pesos secos da parte aérea e das raízes. Os resultados obtidos indicam que o tubete PET-2,5L é o que proporciona o melhor desenvolvimento do porta-enxerto de bacuri