939 research outputs found
Oscillatory flow reactor: A solution for continuous bioprocessing
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Unified description of the dc conductivity of monolayer and bilayer graphene at finite densities based on resonant scatterers
We show that a coherent picture of the dc conductivity of monolayer and
bilayer graphene at finite electronic densities emerges upon considering that
strong short-range potentials are the main source of scattering in these two
systems. The origin of the strong short-range potentials may lie in adsorbed
hydrocarbons at the surface of graphene. The equivalence among results based on
the partial-wave description of scattering, the Lippmann-Schwinger equation,
and the T-matrix approach is established. Scattering due to resonant impurities
close to the neutrality point is investigated via a numerical computation of
the Kubo formula using a kernel polynomial method. We find that relevant
adsorbate species originate impurity bands in monolayer and bilayer graphene
close to the Dirac point. In the midgap region, a plateau of minimum
conductivity of about (per layer) is induced by the resonant disorder.
In bilayer graphene, a large adsorbate concentration can develop an energy gap
between midgap and high-energy states. As a consequence, the conductivity
plateau is supressed near the edges and a "conductivity gap" takes place.
Finally, a scattering formalism for electrons in biased bilayer graphene,
taking into account the degeneracy of the spectrum, is developed and the dc
conductivity of that system is studied.Comment: 25 pages, 13 figures. published version: appendixes improved,
references added, abstract and title slightly changed, plus other minor
revision
Effect of charged line defects on conductivity in graphene: Numerical Kubo and analytical Boltzmann approaches
Charge carrier transport in single-layer graphene with one-dimensional
charged defects is studied theoretically. Extended charged defects, considered
an important factor for mobility degradation in chemically-vapor-deposited
graphene, are described by a self-consistent Thomas-Fermi potential. A
numerical study of electronic transport is performed by means of a
time-dependent real-space Kubo approach in honeycomb lattices containing
millions of carbon atoms, capturing the linear response of realistic size
systems in the highly disordered regime. Our numerical calculations are
complemented with a kinetic transport theory describing charge transport in the
weak scattering limit. The semiclassical transport lifetimes are obtained by
computing scattered amplitudes within the second Born approximation. The
transport electron-hole asymmetry found in the semiclassical approach is
consistent with the Kubo calculations. In the strong scattering regime, the
conductivity is found to be a sublinear function of electronic density and
weakly dependent on the Thomas-Fermi screening wavelength. We attribute this
atypical behavior to the extended nature of one-dimensional charged defects.
Our results are consistent with recent experimental reports.Comment: 15 pages, 9 figure
Avaliação agronômica de variedades de milho de polinização aberta no Rio Grande do Sul.
bitstream/item/175417/1/Boletim-246.pd
European Stroke Organisation (ESO) guideline on screening for subclinical atrial fibrillation after stroke or transient ischaemic attack of undetermined origin
We aimed to provide practical recommendations for the screening of subclinical atrial fibrillation (AF) in patients with ischaemic stroke or transient ischaemic attack (TIA) of undetermined origin. These guidelines are based on the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) methodology. Five relevant Population, Intervention, Comparator, Outcome questions were defined by a multidisciplinary module working group (MWG). Longer duration of cardiac rhythm monitoring increases the detection of subclinical AF, but the optimal monitoring length is yet to be defined. We advise longer monitoring to increase the rate of anticoagulation, but whether longer monitoring improves clinical outcomes needs to be addressed. AF detection does not differ from in- or out-patient ECG-monitoring with similar monitoring duration, so we consider it reasonable to initiate in-hospital monitoring as soon as possible and continue with outpatient monitoring for more than 48 h. Although insertable loop recorders (ILR) increase AF detection based on their longer monitoring duration, comparison with non-implantable ECG devices for similar monitoring time is lacking. We suggest the use of implantable devices, if feasible, for AF detection instead of non-implantable devices to increase the detection of subclinical AF. There is weak evidence of a useful role for blood, ECG and brain imaging biomarkers for the identification of patients at high risk of AF. In patients with patent foramen ovale, we found insufficient evidence from RCT, but prolonged cardiac monitoring in patients >55 years is advisable for subclinical AF detection. To conclude, in adult patients with ischaemic stroke or TIA of undetermined origin, we recommend longer duration of cardiac rhythm monitoring of more than 48 h and if feasible with IRL to increase the detection of subclinical AF
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