264 research outputs found
Transport Length Scales in Disordered Graphene-based Materials: Strong Localization Regimes and Dimensionality Effects
We report on a numerical study of quantum transport in disordered two
dimensional graphene and graphene nanoribbons. By using the Kubo and the
Landauer approaches, transport length scales in the diffusive (mean free path,
charge mobilities) and localized regimes (localization lengths) are computed,
assuming a short range disorder (Anderson-type). In agreement with localization
scaling theory, the electronic systems are found to undergo a conventional
Anderson localization in the zero temperature limit. Localization lengths in
weakly disordered ribbons are found to differ by two orders of magnitude
depending on their edge symmetry, but always remain several orders of magnitude
smaller than those computed for 2D graphene for the same disorder strength.
This pinpoints the role of transport dimensionality and edge effects.Comment: 4 pages, Phys. rev. Lett. (in press
Transport properties of 2D graphene containing structural defects
We propose an extensive report on the simulation of electronic transport in
2D graphene in presence of structural defects. Amongst the large variety of
such defects in sp carbon-based materials, we focus on the Stone-Wales
defect and on two divacancy-type reconstructed defects. First, based on ab
initio calculations, a tight-binding model is derived to describe the
electronic structure of these defects. Then, semiclassical transport properties
including the elastic mean free paths, mobilities and conductivities are
computed using an order-N real-space Kubo-Greenwood method. A plateau of
minimum conductivity () is progressively
observed as the density of defects increases. This saturation of the decay of
conductivity to is associated with defect-dependent
resonant energies. Finally, localization phenomena are captured beyond the
semiclassical regime. An Anderson transition is predicted with localization
lengths of the order of tens of nanometers for defect densities around 1%.Comment: 17 pages, 17 figures, submitted to Phys. Rev.
Anomalous Anisotropic Diffusion Dynamics of Hydration Water at Lipid Membranes
The diffusional water dynamics in the hydration layer of a
dipalmitoylphosphatidylcholine bilayer is studied using molecular dynamics
simulations. By mapping the perpendicular water motion on the ordinary
diffusion equation, we disentangle free energetic and friction effects and
show that perpendicular diffusion is strongly reduced. The lateral water
motion exhibits anomalous diffusion up to several nanoseconds and is
characterized by even further decreased diffusion coefïŹcients, which by
comparison with coarse grained simulations are explained by the transient
corrugated effective free energy landscape imposed by the lipids. This is in
contrast to homogenous surfaces, where boundary hydrodynamic theory
quantitatively predicts the anisotropy of water diffusion
Seabed geoacoustic characterization and classification by multisonar fusion
International audienceThis paper deals with potentialities of improvement of seabed geoacoustic properties characterization and classification by multisensor fusion. The aim of this work is to improve the performance prediction of low frequencies sonar (Anti Submarine Warfare). Geoacoustic and scattering properties estimation by inversion of received acoustic signals remains very difficult and strongly dependent on the system of measurement. Indeed the interaction between an acoustic wave and the sediment is heavily dependent on frequency, measurement angle and micro roughness of seafloor. The fusion of geoacoustic models inverted from different sonar systems with wide diversity of insonification angles and frequencies (single beam echosounder, multibeam echosounder, sidescan sonar and subbottom profiler) allow an extended description of the acoustic properties of the seafloor and the first sediment layers. A characterization method based on the Dempster Shafer theory of evidence is used to fuse geoacoustic models in order to classify the seafloor in three homogeneous acoustic zones (scattered solid, reflective fluid and absorbent fluid). Then, estimation of the geoacoustic parameters is conducted on each zone
Atomistic Boron-Doped Graphene Field Effect Transistors: A Route towards Unipolar Characteristics
We report fully quantum simulations of realistic models of boron-doped
graphene-based field effect transistors, including atomistic details based on
DFT calculations. We show that the self-consistent solution of the
three-dimensional (3D) Poisson and Schr\"odinger equations with a
representation in terms of a tight-binding Hamiltonian manages to accurately
reproduce the DFT results for an isolated boron-doped graphene nanoribbon.
Using a 3D Poisson/Schr\"odinger solver within the Non-Equilibrium Green's
Functions (NEGF) formalism, self-consistent calculations of the gate-screened
scattering potentials induced by the boron impurities have been performed,
allowing the theoretical exploration of the tunability of transistor
characteristics. The boron-doped graphene transistors are found to approach
unipolar behavior as the boron concentration is increased, and by tuning the
density of chemical dopants the electron-hole transport asymmetry can be finely
adjusted. Correspondingly, the onset of a mobility gap in the device is
observed. Although the computed asymmetries are not sufficient to warrant
proper device operation, our results represent an initial step in the direction
of improved transfer characteristics and, in particular, the developed
simulation strategy is a powerful new tool for modeling doped graphene
nanostructures.Comment: 7 pages, 5 figures, published in ACS Nan
Auditing the Editor: A Review of Key Translational Issues in Epigenetic Editing
Currently, most advances in site-specific epigenetic editing for human use are concentrated in basic research, yet, there is considerable interest to translate this technology beyond the bench. This review highlights recent developments with epigenetic editing technology in comparison with the canonical CRISPR-Cas genome editing, as well as the epistemic and ethical considerations with preemptive translation of epigenetic editing into clinical or commercial use in humans. Key considerations in safety, equity, and access to epigenetic editing are highlighted, with a spotlight on the ethical, legal, and social issues of this technology in the context of global health equity
Two-Dimensional Graphene with Structural Defects: Elastic Mean Free Path, Minimum Conductivity, and Anderson Transition
4 pĂĄginas, 4 figuras.-- PACS numbers: 73.23. b, 72.15.Rn, 73.43.Qt.-- et al.Quantum transport properties of disordered graphene with structural defects (Stone-Wales and divacancies) are investigated using a realistic Ï-Ï* tight-binding model elaborated from ab initio calculations. Mean free paths and semiclassical conductivities are then computed as a function of the nature and density of defects (using an order-N real-space Kubo-Greenwood method). By increasing the defect density, the decay of the semiclassical conductivities is predicted to saturate to a minimum value of 4e2/Ïh over a large range (plateau) of carrier density (>0.5Ă1014ââcm-2). Additionally, strong contributions of quantum interferences suggest that the Anderson localization regime could be experimentally measurable for a defect density as low as 1%.J.-C. C. and A. L. acknowledge financial support from
the FNRS of Belgium. Parts of this work are connected to
the Belgian Program on Interuniversity Attraction Poles
(PAI6), to the NanoHymo ARC, to the ETSF e-I3 project
(Grant No. 211956), and to the NANOSIM-GRAPHENE
Project No. ANR-09-NANO-016-01.Peer reviewe
First Computation of Parasitic Fields in LHC Dipole Magnet Interconnects
The Large Hadron Collider (LHC), now under construction at CERN, will rely on about 1600 main superconducting dipole and quadrupole magnets and over 7400 superconducting corrector magnets distributed around the eight sectors of the machine. Each magnet type is powered by dedicated superconducting busbars running along the sectors and mounted on the iron yokes of the main dipole and quadruple magnets. In the numerous magnet interconnects, the busbars are not magnetically shielded from the beam pipes and produce parasitic fields that can affect beam optics. We review the 3-D models that have been developed with ROXIE to compute the parasitic fields and we discuss their potential impacts on machine performance
Quantum Transport Length Scales in Silicon-based Semiconducting Nanowires: Surface Roughness Effects
We report on a theoretical study of quantum charge transport in atomistic
models of silicon nanowires with surface roughness-based disorder. Depending on
the nanowires features (length, roughness profile) various conduction regimes
are explored numerically by using efficient real space order N computational
approaches of both Kubo-Greenwood and Landauer-Buttiker transport frameworks.
Quantitative estimations of the elastic mean free paths, charge mobilities and
localization lengths are performed as a function of the correlation length of
the surface roughness disorder. The obtained values for charge mobilities well
compare with the experimental estimates of the most performant undoped
nanowires. Further the limitations of the Thouless relationship between the
mean free path and the localization length are outlined.Comment: 13 pages, to appear in PR
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