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

One-dimensional Silicon and Germanium Nanostructures With No Carbon Analogues

In this work we report new silicon and germanium tubular nanostructures with no corresponding stable carbon analogues. The electronic and mechanical properties of these new tubes were investigated through ab initio methods. Our results show that the structures have lower energy than their corresponding nanoribbon structures and are stable up to high temperatures (500 and 1000 K, for silicon and germanium tubes, respectively). Both tubes are semiconducting with small indirect band gaps, which can be significantly altered by both compressive and tensile strains. Large bandgap variations of almost 50% were observed for strain rates as small as 3%, suggesting possible applications in sensor devices. They also present high Young's modulus values (0.25 and 0.15 TPa, respectively). TEM images were simulated to help the identification of these new structures

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

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

CARMA1 is a novel regulator of T-ALL disease and leukemic cell migration to the CNS

No abstract available

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

Structure and Dynamics of Boron Nitride Nanoscrolls

Carbon nanoscrolls (CNSs) are structures formed by rolling up graphene layers into a papyruslike shape. CNNs have been experimentally produced by different groups. Boron nitride nanoscrolls (BNNSs) are similar structures using boron nitride instead of graphene layers. In this work we report molecular mechanics and molecular dynamics results for the structural and dynamical aspects of BNNS formation. Similarly to CNS, BNNS formation is dominated by two major energy contributions, the increase in the elastic energy and the energetic gain due to van der Waals interactions of the overlapping surface of the rolled layers. The armchair scrolls are the most stable configuration while zigzag scrolls are metastable structures which can be thermally converted to armchair. Chiral scrolls are unstable and tend to evolve to zigzag or armchair configurations depending on their initial geometries. The possible experimental routes to produce BNNSs are also addressed

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