3,694 research outputs found
Spin-dependent beating patterns in thermoelectric properties: Filtering the carriers of the heat flux in a Kondo adatom system
We theoretically investigate the thermoelectric properties of a
spin-polarized two-dimensional electron gas hosting a Kondo adatom hybridized
with an STM tip. Such a setup is treated within the single-impurity Anderson
model in combination with the atomic approach for the Green's functions. Due to
the spin dependence of the Fermi wavenumbers the electrical and thermal
conductances, together with thermopower and Lorenz number reveal beating
patterns as function of the STM tip position in the Kondo regime. In
particular, by tuning the lateral displacement of the tip with respect to the
adatom vicinity, the temperature and the position of the adatom level, one can
change the sign of the Seebeck coefficient through charge and spin. This opens
a possibility of the microscopic control of the heat flux analogously to that
established for the electrical current
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
Do currents shape global patterns of hybrid richness in reef fishes?
Aim: Our main aim was to identify the distribution of, and potential mechanisms underpinning, hybrid-rich zones – regions with a disproportionate number of unique interspecific hybrids. We investigated whether coral reef fish hybrids coincided with factors such as phylogenetic relatedness, biogeographic barriers, species richness, geographic isolation, endemism, and oceanic currents. Location: Global. Time period: Contemporary. Major taxa studied: Coral reef fishes.
Methods: We conducted a literature review and mapping to assess the taxonomic and global prevalence of hybridisation in coral reef fishes. We then fit Generalised additive models using a full-subsets and Bayesian framework to assess which variables are associated with hybrid-rich zones.
Results: We found 143 unique interspecific coral reef fish hybrids involving 204 species – which accounts for approximately 7% of coral reef fish species, indicating that hybridisation is as common in the sea as it is on land. Characteristic coral reef fish families were not homogeneously represented in our dataset, with particularly colourful groups standing out. Mapping our dataset revealed that coral reef fish hybrids are found worldwide, though some ecoregions (e.g., the Christmas and Cocos (Keeling) Islands, South Kuroshio, Hawaii, and Eastern Philippines) are more hybrid-rich than others. Our analysis revealed that mean surface current velocity, phylogenetic relatedness, and geographic isolation were the best predictors of hybrid richness in a given location.
Main conclusions: Phylogenetic distance between coral reef fish species may serve as a pre-condition for hybridisation to occur, lying between introgression and reproductive incompatibility. We also propose a novel mechanism, with oceanic currents driving long-distance larval dispersal events, transporting stray species to geographically remote sinks to maintain hybrid-rich zones
VELOCITY PROFILE VISUALIZATION OF WATER NATURAL PERCOLATION IN A POROUS MEDIUM
This paper aims to show the profile and the behavior of the velocity of the water flow through a porous medium composed of clay and sand aggregated by burning in an oil furnace. The work models mathematics based on the Navier-Stokes differential equation, which represents the behavior of the water velocity flow in porous medium taking into account parameters of a low velocity laminar flow, increased load loss value and Number of Reynolds > 1. Physical phenomena such as porosity, permeability, particles arrangement, radius and wet perimeter are considered in the equation. The study shows the three-dimensional profile of the water percolation velocity which, originated from the capillary phenomenon, causes a sum of the tensions of increased values able to produce cracks in the medium structure. And, differently from filtration phenomenon, which overcomes the capillarity of the medium by the gravitational force or by efforts applied aiming to increase the flow velocity, the natural percolation opposes to the gravity and to the surrounding pressure moving slowly, reaching the flow at 30 and 40 centimeters depending on the permeability of the porous medium
A experiência da metodologia camponês a camponês em territórios de identidade rural no Nordeste do Brasil.
A pesquisa teve por objetivo a promoção da transição agroeocológica em territórios de identidade rural por meio do ajuste da metodologia ?campesino a campesino? visando à promoção do desenvolvimento sustentável e solidário nas condições do Nordeste do Brasil. Foram identificadas famílias agricultoras camponesas com perfil para inserção em redes de transição agroecológica, potenciais promotores de intercâmbios entre elas para a troca de experiências e saberes. O trabalho foi realizado no Território de identidade rural Sul Sergipano localizado nos tabuleiros costeiros do estado de Sergipe. A realização das ações resultou de uma parceria efetiva entre Colegiado Territorial, Empresa Brasileira de Pesquisa Agropecuária (Embrapa), Instituto Nacional de Colonização e Reforma Agrária (INCRA-SE), Movimento dos Trabalhadores Sem Terra (MST), Universidade Federal de Sergipe (UFS), Universidade Federal de Viçosa (UFV) e Centro de Formação e Assistência Comunitária (CFAC). Para a operacionalização do trabalho e ajuste da metodologia foram potencializadas as redes sociais de agroecologia existentes na região. Os resultados referem-se à identificação das principais experiências de transição agroecológica da região, a consolidação das redes existentes e a criação de formas inovadoras de intercâmbio de experiências potencializadas pela metodologia ajustada, então denominada ?camponês a camponês?. Os aprendizados referem-se à forma de construção coletiva necessária para a introdução de conhecimento agroecológico e, principalmente, de conceitos de maior complexidade, como agrofloresta sucessional e, a perspectiva de construção de uma nova abordagem para a extensão rural em agricultura familiar e camponesa em territórios de identidade rural
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