28,735 research outputs found
Universal zero-bias conductance through a quantum wire side-coupled to a quantum dot
A numerical renormalization-group study of the conductance through a quantum
wire side-coupled to a quantum dot is reported. The temperature and the
dot-energy dependence of the conductance are examined in the light of a
recently derived linear mapping between the Kondo-regime temperature-dependent
conductance and the universal function describing the conductance for the
symmetric Anderson model of a quantum wire with an embedded quantum dot. Two
conduction paths, one traversing the wire, the other a bypass through the
quantum dot, are identified. A gate potential applied to the quantum wire is
shown to control the flow through the bypass. When the potential favors
transport through the wire, the conductance in the Kondo regime rises from
nearly zero at low temperatures to nearly ballistic at high temperatures. When
it favors the dot, the pattern is reversed: the conductance decays from nearly
ballistic to nearly zero. When the fluxes through the two paths are comparable,
the conductance is nearly temperature-independent in the Kondo regime, and a
Fano antiresonance in the fixed-temperature plot of the conductance as a
function of the dot energy signals interference. Throughout the Kondo regime
and, at low temperatures, even in the mixed-valence regime, the numerical data
are in excellent agreement with the universal mapping.Comment: 12 pages, with 9 figures. Submitted to PR
Newtonian View of General Relativistic Stars
Although general relativistic cosmological solutions, even in the presence of
pressure, can be mimicked by using neo-Newtonian hydrodynamics, it is not clear
whether there exists the same Newtonian correspondence for spherical static
configurations. General relativity solutions for stars are known as the
Tolman-Oppenheimer-Volkoff (TOV) equations. On the other hand, the Newtonian
description does not take into account the total pressure effects and therefore
can not be used in strong field regimes. We discuss how to incorporate pressure
in the stellar equilibrium equations within the neo-Newtonian framework. We
compare the Newtonian, neo-Newtonian and the full relativistic theory by
solving the equilibrium equations for both three approaches and calculating the
mass-radius diagrams for some simple neutron stars equation of state.Comment: 6 pages, 3 figures. v2 matches accepted version (EPJC
Thermal dependence of the zero-bias conductance through a nanostructure
We show that the conductance of a quantum wire side-coupled to a quantum dot,
with a gate potential favoring the formation of a dot magnetic moment, is a
universal function of the temperature. Universality prevails even if the
currents through the dot and the wire interfere. We apply this result to the
experimental data of Sato et al.[Phys. Rev. Lett. 95, 066801 (2005)].Comment: 6 pages, 3 figures. More detailed presentation, and updated
references. Final version
Hydrogels in the treatment of rheumatoid arthritis: drug delivery systems and artificial matrices for dynamic in vitro models
Rheumatoid arthritis (RA) is an autoimmune and chronic inflammatory disorder that mostly affects the synovial joints and can promote both cartilage and bone tissue destruction. Several conservative treatments are available to relieve pain and control the inflammation; however, traditional drugs administration are not fully effective and present severe undesired side effects. Hydrogels are a very attractive platform as a drug delivery system to guarantee these handicaps are reduced, and the therapeutic effect from the drugs is maximized. Furthermore, hydrogels can mimic the physiological microenvironment and have the mechanical behavior needed for use as cartilage in vitro model. The testing of these advanced delivery systems is still bound to animal disease models that have shown low predictability. Alternatively, hydrogel-based human dynamic in vitro systems can be used to model diseases, bypassing some of the animal testing problems. RA dynamic disease models are still in an embryonary stage since advances regarding healthy and inflamed cartilage models are currently giving the first steps regarding complexity increase. Herein, recent studies using hydrogels in the treatment of RA, featuring different hydrogel formulations are discussed. Besides, their use as artificial extracellular matrices in dynamic in vitro articular cartilage is also reviewed.Norte2020 project (NORTE-08-5369-FSE000044) and the Portuguese Foundation for Science and Technology (FCT) program (PD/BD/143081/2018). IFC thanks the TERM RES-Hub, Tissue Engineering and Regenerative Medicine Infrastructure project, funded by FCT. The FCT distinction attributed to JMO under the Investigator FCT program (number IF/01285/2015) is also greatly acknowledge
Avaliação da produção e de doenças em genótipos de mandioca em área de várzea do Rio Solimões.
As podridões radiculares em mandioca (Manihot esculenta Grantz) têm ocasionado sérios problemas na produção de mandioca no Estado do Amazonas. Os sintomas manifestam-se em plantas jovens e adultas afetando a região do colo, raiz e haste. O objetivo da pesquisa foi avaliar a produção de raiz e a ocorrência de podridões radiculares em genótipos de mandioca do Banco Ativo de Germoplasma (BAG) na área de várzea do Rio Solimões, do Campo Experimental do Caldeirão, pertencente à Embrapa Amazônia Ocidental. O levantamento da incidência da doença foi por meio da identificação visual na planta e raiz. Foram avaliados 67 genótipos, dos quais 21 se destacaram. Destes, 42,8% permaneceram com as 10 plantas/parcela, enquanto nos demais (57,2%) morreu apenas uma planta. Entre os genótipos que se destacaram, constatou-se que as infecções na planta e raiz foi maior com os fungos Phytophthora drechsleri + Fusarium sp. (42,9%), seguida por P. drechsleri (38,1%) e sadias (19,0%). Os acessos IM-1688; IM-1995; IM-2007 e IM-2042 não apresentaram raiz podre
Influência do período de colheita na produção de raiz e fécula de mandioca (Manihot esculenta Crantz) no Amazonas.
Este trabalho teve como objetivo selecionar cultivares de mandioca com melhor desempenho produtivo, submetidas a duas épocas de colheita em condições de terra firme no Amazonas
A semiquantitative approach to the impurity-band-related transport properties of GaMnAs nanolayers
We investigate the spin-polarized transport of GaMnAs nanolayers in which a
ferromagnetic order exists below a certain transition temperature. Our
calculation for the self-averaged resistivity takes into account the existence
of an impurity band determining the extended ("metallic" transport) or
localized (hopping by thermal excitation) nature of the states at and near the
Fermi level. Magnetic order and resistivity are inter-related due to the
influence of the spin polarization of the impurity band and the effect of the
Zeeman splitting on the mobility edge. We obtain, for a given range of Mn
concentration and carrier density, a "metallic" behavior in which the transport
by extended carriers dominates at low temperature, and is dominated by the
thermally excited localized carriers near and above the transition temperature.
This gives rise to a conspicuous hump of the resistivity which has been
experimentally observed and brings light onto the relationship between
transport and magnetic properties of this material
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