A Brief Review on Syntheses, Structures and Applications of Nanoscrolls

Nanoscrolls are papyrus-like nanostructures which present unique properties due to their open ended morphology. These properties can be exploited in a plethora of technological applications, leading to the design of novel and interesting devices. During the past decade, significant advances in the synthesis and characterization of these structures have been made, but many challenges still remain. In this mini review we provide an overview on their history, experimental synthesis methods, basic properties and application perspectives

Curved Graphene Nanoribbons: Structure and Dynamics of Carbon Nanobelts

Carbon nanoribbons (CNRs) are graphene (planar) structures with large aspect ratio. Carbon nanobelts (CNBs) are small graphene nanoribbons rolled up into spiral-like structures, i. e., carbon nanoscrolls (CNSs) with large aspect ratio. In this work we investigated the energetics and dynamical aspects of CNBs formed from rolling up CNRs. We have carried out molecular dynamics simulations using reactive empirical bond-order potentials. Our results show that similarly to CNSs, CNBs formation is dominated by two major energy contribution, the increase in the elastic energy due to the bending of the initial planar configuration (decreasing structural stability) and the energetic gain due to van der Waals interactions of the overlapping surface of the rolled layers (increasing structural stability). Beyond a critical diameter value these scrolled structures can be even more stable (in terms of energy) than their equivalent planar configurations. In contrast to CNSs that require energy assisted processes (sonication, chemical reactions, etc.) to be formed, CNBs can be spontaneously formed from low temperature driven processes. Long CNBs (length of $\sim$ 30.0 nm) tend to exhibit self-folded racket-like conformations with formation dynamics very similar to the one observed for long carbon nanotubes. Shorter CNBs will be more likely to form perfect scrolled structures. Possible synthetic routes to fabricate CNBs from graphene membranes are also addressed

Mechanical Properties and Fracture Dynamics of Silicene Membranes

As graphene became one of the most important materials today, there is a renewed interest on others similar structures. One example is silicene, the silicon analogue of graphene. It share some the remarkable graphene properties, such as the Dirac cone, but presents some distinct ones, such as a pronounced structural buckling. We have investigated, through density functional based tight-binding (DFTB), as well as reactive molecular dynamics (using ReaxFF), the mechanical properties of suspended single-layer silicene. We calculated the elastic constants, analyzed the fracture patterns and edge reconstructions. We also addressed the stress distributions, unbuckling mechanisms and the fracture dependence on the temperature. We analysed the differences due to distinct edge morphologies, namely zigzag and armchair

Dynamical Aspects Of The Unzipping Of Multiwalled Boron Nitride Nanotubes.

Boron nitride nanoribbons (BNNRs) exhibit very interesting magnetic properties, which could be very useful in the development of spintronic based devices. One possible route to obtain BNNRs is through the unzipping of boron nitride nanotubes (BNNTs), which have been already experimentally realized. In this work, different aspects of the unzipping process of BNNTs were investigated through fully atomistic molecular dynamics simulations using a classical reactive force field (ReaxFF). We investigated multiwalled BNNTs of different diameters and chiralities. Our results show that chirality plays a very important role in the unzipping process, as well as the interlayer coupling. These combined aspects significantly change the fracturing patterns and several other features of the unzipping processes in comparison to the ones observed for carbon nanotubes. Also, similar to carbon nanotubes, defective BNNTs can create regions of very high curvature which can act as a path to the unzipping process.1519147-5

Rotação adequada.

Entre os fatores capazes de proporcionar redução na produtividade das culturas encontram-se as plantas daninhas, que podem afetar a produção agrícola e econômica devido, principalmente, às interferências negativas impostas por sua presença, como a competição por água, nutrientes, luz e efeitos alelopáticos. Atualmente, o controle de plantas daninhas se dá, predominantemente, pelo método químico, com a aplicação de herbicidas. No entanto, essa medida utilizada isoladamente não é suficiente para eliminar toda a interferência das plantas daninhas sobre as culturas, exigindo medidas integradas de controle. A execução de um programa de manejo integrado de plantas daninhas prevê o pleno atendimento a quatro etapas de planejamento: o diagnóstico do problema, a escolha do método a ser utilizado, a seleção e, por último, a avaliação do programa de controle. A prática de pousio para o controle de plantas daninhas tem uma longa história de sucesso, especialmente quando imperava o cultivo convencional. A não movimentação do solo, a cobertura vegetal permanente e a rotação de culturas, preconizadas no Sistema Plantio Direto (SPD), podem resultar em menor germinação das sementes no solo. De acordo com a espécie e a quantidade dessa cobertura, substâncias alelopáticas (inibidoras da germinação ou desenvolvimento de outras espécies) e o efeito do sombreamento determinam variações na intensidade e frequência de emergência das espécies daninhas. Neste sentido, trabalhos sugerem que culturas de entressafra podem ser supressoras das plantas daninhas, assim como sistemas alternados, como o safra ? safrinha, safra ? adubo verde e, mais recentemente, a Integração Lavoura Pecuária Floresta (iLPF), método que consiste na coexistência parcial de uma cultura graníferas e uma forrageira, onde a pastagem permanece na área por toda a entressafra. O levantamento de espécies daninhas, por amostragens da flora emergente, deve permitir a identificação e a quantificação das plantas infestantes, bem como a determinação da sua evolução. Esses conhecimentos podem ser usados para indicar a necessidade de controle, adequando diferentes manejos de solo, da cultura e as sucessões utilizadas buscando a racionalização de uso de herbicidas, com base em considerações de custo/benefício do sistema de produção agrícola. Em função disso, a Techfield, em parceria com os professores e pesquisadores, realiza estudos em diferentes sistemas de produção de grãos e rotações de culturas, com o objetivo de constatar a influência da dinâmica de ocorrência e controle de plantas daninhas destas rotações, o que pode acarretar em redução da utilização de herbicidas

Idealized Carbon-Based Materials Exhibiting Record Deliverable Capacities for Vehicular Methane Storage

Materials for vehicular methane storage have been extensively studied, although no suitable material has been found. In this work, we use molecular simulation to investigate three types of carbon-based materials, Schwarzites, layered graphenes, and carbon nanoscrolls, for use in vehicular methane storage under adsorption conditions of 65 bar and 298 K and desorption conditions of 5.8 bar and 358 K. Ten different Schwarzites were tested and found to have high adsorption with maximums at 273 VSTP/V, but middling deliverable capacities of no more than 131 VSTP/V. Layered graphene and graphene nanoscrolls were found to have extremely high CH4 adsorption capacities of 355 and 339 VSTP/V, respectively, when the interlayer distance was optimized to 11 Å. The deliverable capacities of perfectly layered graphene and graphene nanoscrolls were also found to be exceptional with values of 266 and 252 VSTP/V, respectively, with optimized interlayer distances. These values make idealized graphene and nanoscrolls the record holders for adsorption and deliverable capacities under vehicular methane storage conditions

AFLOW-CHULL: Cloud-Oriented Platform for Autonomous Phase Stability Analysis

A priori prediction of phase stability of materials is a challenging practice, requiring knowledge of all energetically-competing structures at formation conditions. Large materials repositories - housing properties of both experimental and hypothetical compounds - offer a path to prediction through the construction of informatics-based, ab-initio phase diagrams. However, limited access to relevant data and software infrastructure has rendered thermodynamic characterizations largely peripheral, despite their continued success in dictating synthesizability. Herein, a new module is presented for autonomous thermodynamic stability analysis implemented within the open-source, ab-initio framework AFLOW. Powered by the AFLUX Search-API, AFLOW-CHULL leverages data of more than 1.8 million compounds currently characterized in the AFLOW.org repository and can be employed locally from any UNIX-like computer. The module integrates a range of functionality: the identification of stable phases and equivalent structures, phase coexistence, measures for robust stability, and determination of decomposition reactions. As a proof-of-concept, thorough thermodynamic characterizations have been performed for more than 1,300 binary and ternary systems, enabling the identification of several candidate phases for synthesis based on their relative stability criterion - including 18 promising C15b-type structures and two half-Heuslers. In addition to a full report included herein, an interactive, online web application has been developed showcasing the results of the analysis, and is located at aflow.org/aflow-chull

Beta-alanine did not improve high-intensity performance throughout simulated road cycling

This study investigated the effect of beta-alanine supplementation on short-duration sprints and final 4-km simulated uphill cycling time-trial performance during a comprehensive and novel exercise protocol representative of the demands of road-race cycling, and determined if changes were related to increases in muscle carnosine content. Seventeen cyclists (age 38 ± 9 y, height 1.76 ± 0.07 m, body mass 71.4 ± 8.8 kg, V̇O2max 52.4 ± 8.3 ml·kg−1·min−1) participated in this placebo-controlled, double-blind study. Cyclists undertook a prolonged intermittent cycling protocol lasting 125 min, with a 10-s sprint every 20 min, finishing with a 4-km time-trial at 5% simulated incline. Participants completed two familiarization sessions, and two main sessions, one pre-supplementation and one post-supplementation following 28 days of 6.4 g·day−1 of beta-alanine (N=11) or placebo (N=6; maltodextrin). Muscle biopsies obtained pre- and post-supplementation were analysed for muscle carnosine content. There were no main effects on sprint performance throughout the intermittent cycling test (all P>0.05). There was no group (P=0.69), time (P=0.50) or group x time interaction (P=0.26) on time-to-complete the 4-km time-trial. Time-to-completion did not change from pre- to post-supplementation for BA (−19.2 ± 45.6 s, P=0.43) or PL (+2.8 ± 31.6 s, P=0.99). Beta-alanine supplementation increased muscle carnosine content from pre- to post-supplementation (+9.4 ± 4.0 mmol·kg−1dm; P10 min) high-intensity activity throughout endurance cycling may not be improved with beta-alanine supplementation despite increases in muscle carnosine content

The AFLOW Fleet for Materials Discovery

The traditional paradigm for materials discovery has been recently expanded to incorporate substantial data driven research. With the intent to accelerate the development and the deployment of new technologies, the AFLOW Fleet for computational materials design automates high-throughput first principles calculations, and provides tools for data verification and dissemination for a broad community of users. AFLOW incorporates different computational modules to robustly determine thermodynamic stability, electronic band structures, vibrational dispersions, thermo-mechanical properties and more. The AFLOW data repository is publicly accessible online at aflow.org, with more than 1.7 million materials entries and a panoply of queryable computed properties. Tools to programmatically search and process the data, as well as to perform online machine learning predictions, are also available.Comment: 14 pages, 8 figure

Mechanical properties and fracture patterns of graphene (graphitic) nanowiggles

publisher: Elsevier articletitle: Mechanical properties and fracture patterns of graphene (graphitic) nanowiggles journaltitle: Carbon articlelink: http://dx.doi.org/10.1016/j.carbon.2017.04.018 content_type: article copyright: © 2017 Elsevier Ltd. All rights reserved.publisher: Elsevier articletitle: Mechanical properties and fracture patterns of graphene (graphitic) nanowiggles journaltitle: Carbon articlelink: http://dx.doi.org/10.1016/j.carbon.2017.04.018 content_type: article copyright: © 2017 Elsevier Ltd. All rights reserved.This work was supported in part by the Brazilian Agencies CNPq, CAPES and FAPESP. The authors would like to thank the Center for Computational Engineering and Sciences at Unicamp for financial support through the FAPESP/CEPID Grant 2013/08293-7. N.M.P. is supported by the European Research Council PoC 2015 “Silkene” No. 693670, by the European Commission H2020 under the Graphene Flagship Core 1 No. 696656 (WP14 “Polymer Nanocomposites”) and under the Fet Proactive “Neurofibres” No. 732344