4,502 research outputs found
The graphene sheet versus the 2DEG: a relativistic Fano spin-filter via STM and AFM tips
We explore theoretically the density of states (LDOS) probed by an STM tip of
2D systems hosting an adatom and a subsurface impurity,both capacitively
coupled to AFM tips and traversed by antiparallel magnetic fields. Two kinds of
setups are analyzed, a monolayer of graphene and a two-dimensional electron gas
(2DEG). The AFM tips set the impurity levels at the Fermi energy, where two
contrasting behaviors emerge: the Fano factor for the graphene diverges, while
in the 2DEG it approaches zero. As result, the spin-degeneracy of the LDOS is
lifted exclusively in the graphene system, in particular for the asymmetric
regime of Fano interference. The aftermath of this limit is a counterintuitive
phenomenon, which consists of a dominant Fano factor due to the subsurface
impurity even with a stronger STM-adatom coupling. Thus we find a full
polarized conductance, achievable just by displacing vertically the position of
the STM tip. To the best knowledge, our work is the first to propose the Fano
effect as the mechanism to filter spins in graphene. This feature arises from
the massless Dirac electrons within the band structure and allows us to employ
the graphene host as a relativistic Fano spin-filter
Microplastic incorporation into soil in agroecosystems
Background: We live in a plastic age (Thompson et al., 2009), with
microplastic (typically defined as plastic particles < 5 mm) becoming an
increasingly appreciated aspect of environmental pollution. Research has been
overwhelmingly focused on aquatic systems, especially the oceans, but there is
a current shift to more strongly consider terrestrial ecosystems (Rillig,
2012; Horton et al., 2017). In particular agroecosystems are coming into focus
as a major entry point for microplastics in continental systems (Nizzetto et
al., 2016b), where contamination might occur via different sources as sludge
amendment or plastic mulching (Steinmetz et al., 2016). Given the central role
of agroecosystems, including their soil biodiversity (Rillig et al., 2016), in
food production, such numbers are potential cause for concern. Field data on
measured microplastic presence in agricultural soils are still not widely
available, but nevertheless this material is certain to arrive at the soil
surface. The fate of material deposited at the soil surface is not clear:
particles may be removed by wind or water erosion, becoming airborne, or may
be lost by surface runoff (Nizzetto et al., 2016a). Nevertheless, a
substantial part of the microplastic (or nanoplastic following further
disintegration) is expected to enter the soil. The degree of hazard
represented by microplastic to various soil biota is not clear. Direct
evidence comes from experimental work on earthworms, on which microbeads had
negative effects (Huerta Lwanga et al., 2016; also reviewed in Horton et al.,
2017). Data on impacts on other soil biota groups are not available. However,
Kiyama et al. (2012) have shown that polystyrene beads can be taken up by the
nematode Caenorhabditis elegans; this means the material could also accumulate
in the soil food web (Rillig, 2012). Movement into soil is an important aspect
of assessing risk: will soil biota be exposed to microplastics? Here, we
sketch what is known about movement of such particles in soil, which players
and factors could influence this, and we chart avenues for research aimed at
the movement and distribution of microplastic in agricultural soils
Cost-effectiveness analysis of a state funded programme for control of severe asthma
<p>Abstract</p> <p>Background</p> <p>Asthma is one of the most common chronic diseases and a major economical burden to families and health systems. Whereas efficacy of current therapeutical options has been clearly established, cost-effectiveness analysis of public health interventions for asthma control are scarce.</p> <p>Methods</p> <p>81 patients with severe asthma (12–75 years) joining a programme in a reference clinic providing free asthma medication were asked retrospectively about costs and events in the previous 12 months. During 12 months after joining the programme, information on direct and indirect costs, asthma control by lung function, symptoms and quality of life were collected. The information obtained was used to estimate cost-effectiveness of the intervention as compared to usual public health asthma management. Sensitivity analysis was conducted.</p> <p>Results</p> <p>64 patients concluded the study. During the 12-months follow-up within the programme, patients had 5 fewer days of hospitalization and 68 fewer visits to emergency/non scheduled medical visits per year, on average. Asthma control scores improved by 50% and quality of life by 74%. The annual saving in public resources was US512, and family costs were reduced by US$733.</p> <p>Conclusion</p> <p>A programme for control of severe asthma in a developing country can reduce morbidity, improve quality of life and save resources from the health system and patients families.</p
Catching the Bound States in the Continuum of a Phantom Atom in Graphene
We explore theoretically the formation of bound states in the continuum
(BICs) in graphene hosting two collinear adatoms situated at different sides of
the sheet and at the center of the hexagonal cell, where a phantom atom of a
fictitious lattice emulates the six carbons of the cell. We verify that in this
configuration the local density of states (LDOS) near the Dirac points exhibits
two characteristic features: i) the cubic dependence on energy instead of the
linear one for graphene as found in New J. Phys. 16, 013045 (2014) and ii)
formation of BICs as aftermath of a Fano destructive interference assisted by
the Coulomb correlations in the adatoms. For the geometry where adatoms are
collinear to carbon atoms, we report absence of BICs
Quantum phase transition triggering magnetic BICs in graphene
Graphene hosting a pair of collinear adatoms in the phantom atom
configuration has pseudogap with cubic scaling on energy,
which leads to the appearance of
spin-degenerate bound states in the continuum (BICs) [Phys. Rev. B 92, 045409
(2015)]. In the case when adatoms are locally coupled to a single carbon atom
the pseudogap scales linearly with energy, which prevents the formation of
BICs. In this Letter, we explore the effects of non-local coupling
characterized by the Fano factor of interference tunable by changing
the slope of the Dirac cones in the graphene band-structure. We demonstrate
that three distinct regimes can be identified: i) for (critical
point) a mixed pseudogap appears
yielding a phase with spin-degenerate BICs; ii) near when
the system undergoes a quantum phase
transition in which the new phase is characterized by magnetic BICs and iii) at
a second critical value the cubic scaling of the pseudogap with
energy characteristic to the phantom atom
configuration is restored and the phase with non-magnetic BICs is recovered.
The phase with magnetic BICs can be described in terms of an effective
intrinsic exchange field of ferromagnetic nature between the adatoms mediated
by graphene monolayer. We thus propose a new type of quantum phase transition
resulting from the competition between the states characterized by
spin-degenerate and magnetic BICs
Caracterização e análise de acessos do banco ativo de germoplasma de Spondias da Embrapa Mandioca e Fruticultura por meio de descritores morfológicos e agronômicos.
Introdução: O gênero Spondias abriga várias frutíferas arbóreas, com espécies nativas do Brasil. Essas plantas são exploradas por meio do extrativismo, com grande potencial econômico e industrial, visto que apresentam frutos comestíveis, saborosos e com alto teor nutritivo. Contudo, há poucas pesquisas que visam à domesticação ou produção comercial dos frutos de Spondias, dado pela falta de informações genéticas, assim como pela ausência de informações de quem as utiliza. Assim, para utilizar as espécies do gênero Spondias, ampliando seus cultivos, é necessário caracterizar os recursos genéticos. Por isso, a Embrapa conserva essas espécies em um Banco Ativo de Germoplasma (BAG), garantindo a variabilidade genética existente, a fim de serem usadas em programas de melhoramento de plantas. Portanto, a correta caracteri- zação e análise dos acessos são de fundamental importância, podendo ser realizada por meio de descritores morfológicos e agronômicos, permitindo desta forma, a separação entre os acessos. A partir do conhecimen-to da variabilidade genética presente entre os acessos conservados no banco de germoplasma é possível desenvolver produtos pré-tecnológicos, tecnológicos e cultivares de interesse econômico. [...]
Proposta metodológica para unidades demonstrativas e melhoramento participativo de milho e feijão em sistemas agroecológicos.
Ao apresentar esta publicação, reafirmamos a consideração dos autores de que os trabalhos de pesquisa devem se basear, cada vez mais, nas necessi- dades do público que se pretende atingir, notadamente em projetos de pes- quisa e desenvolvimento com enfoque agroecológico, em que ações de ade- quação de métodos de avaliação e de melhoramento participativo devem ser abordados pela importância do desenvolvimento e da produção de sementes agroecológicas. As metodologias de avaliação, utilizadas em sistemas convencionais, devem ser ajustadas para uma avaliação mais precisa e adequada para os sistemas agroecológicos e a estratégias das Unidades Produtivas como uma metodo- logia não somente para demonstração, mas também para avaliação e mos- trar-se uma alternativa viável. Conjuntamente, o desenvolvimento de um novo método de seleção denominado células de seleção permite em um mesmo local a seleção de duas espécies, como o milho e feijão, e rotacionando para um segundo plantio no mesmo ano agrícola, aumentando consideravelmente a eficiência do processo de seleção. O desenvolvimento adequado de estratégias para avaliação e melhoramento para sistemas agroecológicos são fundamentais para os agricultores, bem como para os programas de produção de sementes agroecológicas. Devem- se formular protocolos apropriados junto aos órgãos públicos, tanto para elaboração de legislações apropriadas, como para indicação adequada de cultivares para sistemas de base agroecológica
- …