7,777 research outputs found
May 12 1997 Cme Event: I. a Simplified Model of the Pre-Eruptive Magnetic Structure
A simple model of the coronal magnetic field prior to the CME eruption on May
12 1997 is developed. First, the magnetic field is constructed by superimposing
a large-scale background field and a localized bipolar field to model the
active region (AR) in the current-free approximation. Second, this potential
configuration is quasi-statically sheared by photospheric vortex motions
applied to two flux concentrations of the AR. Third, the resulting force-free
field is then evolved by canceling the photospheric magnetic flux with the help
of an appropriate tangential electric field applied to the central part of the
AR.
To understand the structure of the modeled configuration, we use the field
line mapping technique by generalizing it to spherical geometry. It is
demonstrated that the initial potential configuration contains a hyperbolic
flux tube (HFT) which is a union of two intersecting quasi-separatrix layers.
This HFT provides a partition of the closed magnetic flux between the AR and
the global solar magnetic field. The vortex motions applied to the AR interlock
the field lines in the coronal volume to form additionally two new HFTs pinched
into thin current layers. Reconnection in these current layers helps to
redistribute the magnetic flux and current within the AR in the
flux-cancellation phase. In this phase, a magnetic flux rope is formed together
with a bald patch separatrix surface wrapping around the rope. Other important
implications of the identified structural features of the modeled configuration
are also discussed.Comment: 25 pages, 11 figures, to appear in ApJ 200
Metallic proximity effect in ballistic graphene with resonant scatterers
We study the effect of resonant scatterers on the local density of states in
a rectangular graphene setup with metallic leads. We find that the density of
states in a vicinity of the Dirac point acquires a strong position dependence
due to both metallic proximity effect and impurity scattering. This effect may
prevent uniform gating of weakly-doped samples. We also demonstrate that even a
single-atom impurity may essentially alter electronic states at low-doping on
distances of the order of the sample size from the impurity.Comment: 9 pages, 2 figure
Using of geophysical methods for estimation of the technological properties of ores of pyrite-polymetallic deposits
The complex of well and logging methods providing efficient estimation of the technological properties of the main ore minerals and ores in process of deposits prospecting is developed basing on study of their petrophysical properties. It provides selection of representative technological probes and development on this basis of optimum methods of processing of ores. Formation of physical-geological technological model of the deposit will allow to reduce losses of metals on concentrating repartition
Ballistic charge transport in chiral-symmetric few-layer graphene
A transfer matrix approach to study ballistic charge transport in few-layer
graphene with chiral-symmetric stacking configurations is developed. We
demonstrate that the chiral symmetry justifies a non-Abelian gauge
transformation at the spectral degeneracy point (zero energy). This
transformation proves the equivalence of zero-energy transport properties of
the multilayer to those of the system of uncoupled monolayers. Similar
transformation can be applied in order to gauge away an arbitrary magnetic
field, weak strain, and hopping disorder in the bulk of the sample. Finally, we
calculate the full-counting statistics at arbitrary energy for different
stacking configurations. The predicted gate-voltage dependence of conductance
and noise can be measured in clean multilayer samples with generic metallic
leads.Comment: 6 pages, 5 figures; EPL published versio
Conductance through the disclination dipole defect in metallic carbon nanotubes
The electronic transport properties of a metallic carbon nanotube with the
five-seven disclination pair characterized by a lattice distortion vector are
investigated. The influence of the disclination dipole includes induced
curvature and mixing of two sublattices. Both these factors are taken into
account via a self-consistent perturbation approach. The conductance and the
Fano factor are calculated within the transfer-matrix technique. PACS:
73.63.Fg, 72.80.Rj, 72.10.F
Diffusion and criticality in undoped graphene with resonant scatterers
A general theory is developed to describe graphene with arbitrary number of
isolated impurities. The theory provides a basis for an efficient numerical
analysis of the charge transport and is applied to calculate the minimal
conductivity of graphene with resonant scatterers. In the case of smooth
resonant impurities conductivity grows logarithmically with increasing impurity
concentration, in agreement with renormalization group analysis for the
symmetry class DIII. For vacancies (or strong on-site potential impurities) the
conductivity saturates at a constant value that depends on the vacancy
distribution among two sublattices as expected for the symmetry class BDI.Comment: 4 pages, 2 figure
L\'evy flights due to anisotropic disorder in graphene
We study transport properties of graphene with anisotropically distributed
on-site impurities (adatoms) that are randomly placed on every third line drawn
along carbon bonds. We show that stripe states characterized by strongly
suppressed back-scattering are formed in this model in the direction of the
lines. The system reveals L\'evy-flight transport in stripe direction such that
the corresponding conductivity increases as the square root of the system
length. Thus, adding this type of disorder to clean graphene near the Dirac
point strongly enhances the conductivity, which is in stark contrast with a
fully random distribution of on-site impurities which leads to Anderson
localization. The effect is demonstrated both by numerical simulations using
the Kwant code and by an analytical theory based on the self-consistent
-matrix approximation.Comment: 11 pages, 6 figure
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