Cosmic String Wakes in Scalar-Tensor Gravities

The formation and evolution of cosmic string wakes in the framework of a scalar-tensor gravity are investigated in this work. We consider a simple model in which cold dark matter flows past an ordinary string and we treat this motion in the Zel'dovich approximation. We make a comaprison between our results and previous results obtained in the context of General Relativity. We propose a mechanism in which the contribution of the scalar field to the evolution of the wakes may lead to a cosmological observation.Comment: Replaced version to be published in the Classical and Quantum Gravit

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

Como a planta de arroz se desenvolve.

Planta. Raízes. Caule. Perfilhamento. Folha. Panícula. Espigueta. Flor. Grão. Germinação. Plântula. Fases de crescimento da planta de arroz. Produção de matéria seca. Produção. Características da planta relacionadas com a capacidade de produção. Exigências de radiação solar pela cultura do arroz.bitstream/item/100485/1/Encarte.pdfEncarte

Sistema de produção agrossilvipastorial para a região de caatinga - SAF: avaliação dos impactos econômicos, sociais e ambientais.

bitstream/CNPC-2010/23041/1/cot110.pd

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

Comparison of processes for lithium recovery from lepidolite by H2SO4 digestion or HCl leaching

Lithium is becoming a strategic metal due to its important applications in secondary battery electrodes used in electronic appliances and also in electric traction vehicles. Lithium primary resources are brines and rock minerals, the former being nowadays almost exclusively used in the production of lithium commodities. With the expected increase in lithium demand, the development of competitive technologies for recovery lithium from ores like pegmatites is getting imperative. The high energy and reagents consumption in processing minerals is an issue that should be considered. This paper presents some results on the comparison of two acid treatment routes for lepidolite, the H2SO4 digestion and HCl leaching. Before both chemical treatments, lepidolite was calcined at 800oC and was transformed in a more reactive species, ƒÀ-spodumene. The H2SO4 digestion at 175oC (followed by water leaching) allowed 88% Li recovery into the solution in 30 min. By the contrary, the HCl leaching process carried out at 90oC also achieved similar yields but only after 4 h of reaction. In both cases, an acid excess was used, but clearly higher for the essays with HCl. The H2SO4 digestion process was also advantageous in what concerns to selectivity over other contained metals. Al, Mn and Fe concentrations in solutions were substantially higher in the hydrochloric acid leaching. These results showed that the digestion with sulphuric acid can be a more efficient and competitive process

Minero-metallurgical processes for lithium recovery from pegmatitic ores = Processos minero-metalúrgicos para a recuperação de lítio de minérios pegmatíticos

ABSTRACT: With the expected increase of lithium demand in the forthcoming years, an efficient management of all the available resources is necessary. Rock minerals like pegmatites are important primary sources of lithium that shall be valorized. Minero-metallurgical processes have been developed for lithium recovery from pegmatitic ore deposits, involving physical concentration, thermal treatment, digestion and/or leaching in order to obtain a lithium soluble species adequate to produce lithium carbonate by precipitation. Physical concentration by froth flotation or by optical sorting are the two main alternative operations to produce a Li concentrate. Metallurgical treatment starts by calcination where the silicate structure is transformed to a more reactive solid phase (ß-spodumene). Afterwards digestion with sulfuric acid and water leaching allows the dissolution of lithium sulfate. Carbonate pressure leaching is an alternative technology for treating pegmatites and production of lithium carbonate. Energy and chemicals savings is crucial in order to reduce the high costs associated with metallurgical processing of Li rock minerals.  RESUMO: Com o aumento na procura de lítio nos próximos anos, torna-se necessária uma gestão eficiente de todos os recursos disponíveis. Os minérios pegmatíticos são fontes primárias importantes deste metal que devem ser valorizadas. Neste contexto, têm sido desenvolvidos processos minero-metalúrgicos para a recuperação de lítio, que envolvem a concentração física, o tratamento térmico, a digestão e/ou lixiviação, de forma a obter o lítio em formas solúveis que permitam a posterior produção de carbonato de lítio por precipitação. Na concentração física, as duas principais operações para produzir um concentrado de Li são a flutuação por espumas ou a triagem por processos ópticos. O tratamento metalúrgico começa por uma etapa de calcinação, onde a estrutura original do silicato é transformada numa fase sólida mais reactiva (ß-espodumena). Em seguida, a digestão com ácido sulfúrico e lixiviação com água permite a dissolução do sulfato de lítio. A lixiviação sob pressão usando carbonatos é uma tecnologia alternativa para o tratamento de pegmatitos e produção de carbonato de lítio. A gestão eficiente da energia e do consumo de produtos químicos é crucial para reduzir os elevados custos associados ao processamento metalúrgico de minerais de lítio