245 research outputs found
Magneto-optical Selection Rules in Bilayer Bernal Graphene
The low-frequency magneto-optical properties of bilayer Bernal graphene are
studied by the tight-binding model with four most important interlayer
interactions taken into account. Since the main features of the wave functions
are well depicted, the Landau levels can be divided into two groups based on
the characteristics of the wave functions. These Landau levels lead to four
categories of absorption peaks in the optical absorption spectra. Such
absorption peaks own complex optical selection rules and these rules can be
reasonably explained by the characteristics of the wave functions. In addition,
twin-peak structures, regular frequency-dependent absorption rates and complex
field-dependent frequencies are also obtained in this work. The main features
of the absorption peaks are very different from those in monolayer graphene and
have their origin in the interlayer interactions
In-situ Analysis of Laminated Composite Materials by X-ray Micro-Computed Tomography and Digital Volume Correlation
The complex mechanical behaviour of composite materials, due to internal heterogeneity and multi-layered composition impose deeper studies. This paper presents an experimental investigation technique to perform volume kinematic measurements in composite materials. The association of X-ray micro-computed tomography acquisitions and Digital Volume Correlation (DVC) technique allows the measurement of displacements and deformations in the whole volume of composite specimen. To elaborate the latter, composite fibres and epoxy resin are associated with metallic particles to create contrast during X-ray acquisition.
A specific in situ loading device is presented for three-point bending tests, which enables the visualization of transverse shear effects in composite structures
Warren McCulloch and the British cyberneticians
Warren McCulloch was a significant influence on a number of British cyberneticians, as some British pioneers in this area were on him. He interacted regularly with most of the main figures on the British cybernetics scene, forming close friendships and collaborations with several, as well as mentoring others. Many of these interactions stemmed from a 1949 visit to London during which he gave the opening talk at the inaugural meeting of the Ratio Club, a gathering of brilliant, mainly young, British scientists working in areas related to cybernetics. This paper traces some of these relationships and interaction
Localization of Dirac electrons by Moire patterns in graphene bilayers
We study the electronic structure of two Dirac electron gazes coupled by a
periodic Hamiltonian such as it appears in rotated graphene bilayers. Ab initio
and tight-binding approaches are combined and show that the spatially periodic
coupling between the two Dirac electron gazes can renormalize strongly their
velocity. We investigate in particular small angles of rotation and show that
the velocity tends to zero in this limit. The localization is confirmed by an
analysis of the eigenstates which are localized essentially in the AA zones of
the Moire patterns.Comment: 4 pages, 5 figure
Structural correlations in heterogeneous electron transfer at monolayer and multilayer graphene electrodes
As a new form of carbon, graphene is attracting intense interest as an electrode material with widespread applications. In the present study, the heterogeneous electron transfer (ET) activity of graphene is investigated using scanning electrochemical cell microscopy (SECCM), which allows electrochemical currents to be mapped at high spatial resolution across a surface for correlation with the corresponding structure and properties of the graphene surface. We establish that the rate of heterogeneous ET at graphene increases systematically with the number of graphene layers, and show that the stacking in multilayers also has a subtle influence on ET kinetics. © 2012 American Chemical Society
Persistent currents in carbon nanotubes based rings
Persistent currents in rings constructed from carbon nanotubes are
investigated theoretically. After studying the contribution of finite
temperature or quenched disorder on covalent rings, the complexity due to the
bundle packing is addressed. The case of interacting nanotori and
self-interacting coiled nanotubes are analyzed in details in relation with
experiments.Comment: 7 sections, 9 figure
Electronic properties of bilayer and multilayer graphene
We study the effects of site dilution disorder on the electronic properties
in graphene multilayers, in particular the bilayer and the infinite stack. The
simplicity of the model allows for an easy implementation of the coherent
potential approximation and some analytical results. Within the model we
compute the self-energies, the density of states and the spectral functions.
Moreover, we obtain the frequency and temperature dependence of the
conductivity as well as the DC conductivity. The c-axis response is
unconventional in the sense that impurities increase the response for low
enough doping. We also study the problem of impurities in the biased graphene
bilayer.Comment: 36 pages, 42 figures, references adde
Effect of Layer-Stacking on the Electronic Structure of Graphene Nanoribbons
The evolution of electronic structure of graphene nanoribbons (GNRs) as a
function of the number of layers stacked together is investigated using
\textit{ab initio} density functional theory (DFT) including interlayer van der
Waals interactions. Multilayer armchair GNRs (AGNRs), similar to single-layer
AGNRs, exhibit three classes of band gaps depending on their width. In zigzag
GNRs (ZGNRs), the geometry relaxation resulting from interlayer interactions
plays a crucial role in determining the magnetic polarization and the band
structure. The antiferromagnetic (AF) interlayer coupling is more stable
compared to the ferromagnetic (FM) interlayer coupling. ZGNRs with the AF
in-layer and AF interlayer coupling have a finite band gap while ZGNRs with the
FM in-layer and AF interlayer coupling do not have a band gap. The ground state
of the bi-layer ZGNR is non-magnetic with a small but finite band gap. The
magnetic ordering is less stable in multilayer ZGNRs compared to single-layer
ZGNRs. The quasipartcle GW corrections are smaller for bilayer GNRs compared to
single-layer GNRs because of the reduced Coulomb effects in bilayer GNRs
compared to single-layer GNRs.Comment: 10 pages, 5 figure
Deletion mapping of chromosome 16q in hepatocellular carcinoma
Hepatocellular carcinoma (HCC) frequently shows an allelic imbalance (AI) on chromosome 16q. In order to define the commonly affected regions on chromosome 16q, we assessed AI studies in 41 HCCs using a panel of 37 microsatellite markers. Thirty-five cases (85%) showed AI at one or more loci. Among the 35 cases with AI, 21 cases showed multiple AI, suggesting the wide scope of deletion on the long arm of chromosome 16, and the remaining 14 cases showed partial AI. Detailed deletion mapping identified two independent commonly deleted regions on this chromosome arm. These included the D16S3106 locus and D16S498 locus. In conclusion, we have demonstrated frequent AI on 16q in HCCs and identified two loci with frequent AI, which may harbour new tumour suppressor genes.ope
Energy distributions of field emitted electrons from carbon nanosheets: manifestation of the quantum size effect
We emphasize the importance of experiments with voltage dependent field
emission energy distribution analysis in carbon nanosheets. Our analysis shows
the crucial influence of the band structure on the energy distribution of field
emitted electrons in few-layer graphene. In addition to the main peak we found
characteristic sub-peaks in the energy distribution. Their positions strongly
depend on the number of layers and the inter-layer interaction. The discovery
of these peaks in field emission experiments from carbon nanosheets would be a
clear manifestation of the quantum size effect in these new materials.Comment: accepted for publication in JETP Letter
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