917 research outputs found
Estimulação Magnética Transcraniana na depressão: resultados obtidos com duas aplicações semanais
Electronic transport in polycrystalline graphene
Most materials in available macroscopic quantities are polycrystalline.
Graphene, a recently discovered two-dimensional form of carbon with strong
potential for replacing silicon in future electronics, is no exception. There
is growing evidence of the polycrystalline nature of graphene samples obtained
using various techniques. Grain boundaries, intrinsic topological defects of
polycrystalline materials, are expected to dramatically alter the electronic
transport in graphene. Here, we develop a theory of charge carrier transmission
through grain boundaries composed of a periodic array of dislocations in
graphene based on the momentum conservation principle. Depending on the grain
boundary structure we find two distinct transport behaviours - either high
transparency, or perfect reflection of charge carriers over remarkably large
energy ranges. First-principles quantum transport calculations are used to
verify and further investigate this striking behaviour. Our study sheds light
on the transport properties of large-area graphene samples. Furthermore,
purposeful engineering of periodic grain boundaries with tunable transport gaps
would allow for controlling charge currents without the need of introducing
bulk band gaps in otherwise semimetallic graphene. The proposed approach can be
regarded as a means towards building practical graphene electronics.Comment: accepted in Nature Material
Effect of an acid diet allied to sonic toothbrushing on root dentin permeability: an in vitro study
Evolution of Landau Levels into Edge States at an Atomically Sharp Edge in Graphene
The quantum-Hall-effect (QHE) occurs in topologically-ordered states of
two-dimensional (2d) electron-systems in which an insulating bulk-state
coexists with protected 1d conducting edge-states. Owing to a unique
topologically imposed edge-bulk correspondence these edge-states are endowed
with universal properties such as fractionally-charged quasiparticles and
interference-patterns, which make them indispensable components for QH-based
quantum-computation and other applications. The precise edge-bulk
correspondence, conjectured theoretically in the limit of sharp edges, is
difficult to realize in conventional semiconductor-based electron systems where
soft boundaries lead to edge-state reconstruction. Using scanning-tunneling
microscopy and spectroscopy to follow the spatial evolution of bulk
Landau-levels towards a zigzag edge of graphene supported above a graphite
substrate we demonstrate that in this system it is possible to realize
atomically sharp edges with no edge-state reconstruction. Our results single
out graphene as a system where the edge-state structure can be controlled and
the universal properties directly probed.Comment: 16 pages, 4 figure
Observation of Van Hove singularities in twisted graphene layers
Electronic instabilities at the crossing of the Fermi energy with a Van Hove
singularity in the density of states often lead to new phases of matter such as
superconductivity, magnetism or density waves. However, in most materials this
condition is difficult to control. In the case of single-layer graphene, the
singularity is too far from the Fermi energy and hence difficult to reach with
standard doping and gating techniques. Here we report the observation of
low-energy Van Hove singularities in twisted graphene layers seen as two
pronounced peaks in the density of states measured by scanning tunneling
spectroscopy. We demonstrate that a rotation between stacked graphene layers
can generate Van Hove singularities, which can be brought arbitrarily close to
the Fermi energy by varying the angle of rotation. This opens intriguing
prospects for Van Hove singularity engineering of electronic phases.Comment: 21 pages 5 figure
Strain-induced Evolution of Electronic Band Structures in a Twisted Graphene Bilayer
Here we study the evolution of local electronic properties of a twisted
graphene bilayer induced by a strain and a high curvature. The strain and
curvature strongly affect the local band structures of the twisted graphene
bilayer; the energy difference of the two low-energy van Hove singularities
decreases with increasing the lattice deformations and the states condensed
into well-defined pseudo-Landau levels, which mimic the quantization of massive
Dirac fermions in a magnetic field of about 100 T, along a graphene wrinkle.
The joint effect of strain and out-of-plane distortion in the graphene wrinkle
also results in a valley polarization with a significant gap, i.e., the
eight-fold degenerate Landau level at the charge neutrality point is splitted
into two four-fold degenerate quartets polarized on each layer. These results
suggest that strained graphene bilayer could be an ideal platform to realize
the high-temperature zero-field quantum valley Hall effect.Comment: 4 figure
Evolution of Microscopic Localization in Graphene in a Magnetic Field from Scattering Resonances to Quantum Dots
Graphene is a unique two-dimensional material with rich new physics and great
promise for applications in electronic devices. Physical phenomena such as the
half-integer quantum Hall effect and high carrier mobility are critically
dependent on interactions with impurities/substrates and localization of Dirac
fermions in realistic devices. We microscopically study these interactions
using scanning tunneling spectroscopy (STS) of exfoliated graphene on a SiO2
substrate in an applied magnetic field. The magnetic field strongly affects the
electronic behavior of the graphene; the states condense into welldefined
Landau levels with a dramatic change in the character of localization. In zero
magnetic field, we detect weakly localized states created by the substrate
induced disorder potential. In strong magnetic field, the two-dimensional
electron gas breaks into a network of interacting quantum dots formed at the
potential hills and valleys of the disorder potential. Our results demonstrate
how graphene properties are perturbed by the disorder potential; a finding that
is essential for both the physics and applications of graphene.Comment: to be published in Nature Physic
Efficacy of a specific model for cognitive-behavioral therapy among panic disorder patients with agoraphobia: a randomized clinical trial
The All-Data-Based Evolutionary Hypothesis of Ciliated Protists with a Revised Classification of the Phylum Ciliophora (Eukaryota, Alveolata)
This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article's Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/ The file attached is the published version of the article
Antinociceptive activity of Mentha piperita leaf aqueous extract in mice
Mentha piperita L. (Labiatae) is an herbaceous plant, used in folk medicine for the treatment of several medical disorders.In the present study, the aqueous extract of Mentha piperita leaf, at the i.p doses 200 and 400 mg/kg, showed significant analgesic effects against both acetic acid-induced writhing and hot plate-induced thermal stimulation in mice, with protection values of 51.79% and 20.21% respectively. On the contrary, the Mentha piperita leaf aqueous extract did not exhibit anti-inflammatory activity against carrageenan induced paw oedema.These findings indicate that Mentha piperita has a potential analgesic effect that may possibly have mediated centrally and peripherally, as well as providing a pharmacological evidence for its traditional use as a pain reliever
- …