409 research outputs found
Detection of the Horizontal Divergent Flow prior to the Solar Flux Emergence
It is widely accepted that solar active regions including sunspots are formed
by the emerging magnetic flux from the deep convection zone. In previous
numerical simulations, we found that the horizontal divergent flow (HDF) occurs
before the flux emergence at the photospheric height. This Paper reports the
HDF detection prior to the flux emergence of NOAA AR 11081, which is located
away from the disk center. We use SDO/HMI data to study the temporal changes of
the Doppler and magnetic patterns from those of the reference quiet Sun. As a
result, the HDF appearance is found to come before the flux emergence by about
100 minutes. Also, the horizontal speed of the HDF during this time gap is
estimated to be 0.6 to 1.5 km s^-1, up to 2.3 km s^-1. The HDF is caused by the
plasma escaping horizontally from the rising magnetic flux. And the interval
between the HDF and the flux emergence may reflect the latency during which the
magnetic flux beneath the solar surface is waiting for the instability onset to
the further emergence. Moreover, SMART Halpha images show that the
chromospheric plages appear about 14 min later, located co-spatial with the
photospheric pores. This indicates that the plages are caused by plasma flowing
down along the magnetic fields that connect the pores at their footpoints. One
importance of observing the HDF may be the possibility to predict the sunspot
appearances that occur in several hours.Comment: 32 pages, 8 figures, 3 tables, accepted for publication in Ap
Contact resistivity and current flow path at metal/graphene contact
The contact properties between metal and graphene were examined. The
electrical measurement on a multiprobe device with different contact areas
revealed that the current flow preferentially entered graphene at the edge of
the contact metal. The analysis using the cross-bridge Kelvin structure (CBK)
suggested that a transition from the edge conduction to area conduction
occurred for a contact length shorter than the transfer length of ~1 micron.
The contact resistivity for Ni was measured as ~5*10-6 Ohmcm2 using the CBK. A
simple calculation suggests that a contact resistivity less than 10-9 Ohmcm2 is
required for miniaturized graphene field effect transistors
Magnetic Properties of Solar Active Regions that Govern Large Solar Flares and Eruptions
Solar flares and coronal mass ejections (CMEs), especially the larger ones, emanate from active regions (ARs). With the aim to understand the magnetic properties that govern such flares and eruptions, we systematically survey all flare events with GOES levels of >=M5.0 within 45 deg from disk center between May 2010 and April 2016. These criteria lead to a total of 51 flares from 29 ARs, for which we analyze the observational data obtained by the Solar Dynamics Observatory. More than 80% of the 29 ARs are found to exhibit delta-sunspots and at least three ARs violate Hale's polarity rule. The flare durations are approximately proportional to the distance between the two flare ribbons, to the total magnetic flux inside the ribbons, and to the ribbon area. From our study, one of the parameters that clearly determine whether a given flare event is CME-eruptive or not is the ribbon area normalized by the sunspot area, which may indicate that the structural relationship between the flaring region and the entire AR controls CME productivity. AR characterization show that even X-class events do not require delta-sunspots or strong-field, high-gradient polarity inversion lines. An investigation of historical observational data suggests the possibility that the largest solar ARs, with magnetic flux of 2x10^23 Mx, might be able to produce "superflares" with energies of order of 10^34 erg. The proportionality between the flare durations and magnetic energies is consistent with stellar flare observations, suggesting a common physical background for solar and stellar flares
Competing Ground States of the New Class of Halogen-Bridged Metal Complexes
Based on a symmetry argument, we study the ground-state properties of
halogen-bridged binuclear metal chain complexes. We systematically derive
commensurate density-wave solutions from a relevant two-band Peierls-Hubbard
model and numerically draw the the ground-state phase diagram as a function of
electron-electron correlations, electron-phonon interactions, and doping
concentration within the Hartree-Fock approximation. The competition between
two types of charge-density-wave states, which has recently been reported
experimentally, is indeed demonstrated.Comment: 4 pages, 5 figures embedded, to appear in J. Phys. Soc. Jp
The Relationship Between Plasma Flow Doppler Velocities and Magnetic Field Parameters During the Emergence of Active Regions at the Solar Photospheric Level
A statistical study has been carried out of the relationship between plasma
flow Doppler velocities and magnetic field parameters during the emergence of
active regions at the solar photospheric level with data acquired by the
Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory
(SOHO). We have investigated 224 emerging active regions with different spatial
scales and positions on the solar disc. The following relationships for the
first hours of the emergence of active regions have been analysed: i) of peak
negative Doppler velocities with the position of the emerging active regions on
the solar disc; ii) of peak plasma upflow and downflow Doppler velocities with
the magnetic flux growth rate and magnetic field strength for the active
regions emerging near the solar disc centre (the vertical component of plasma
flows); iii) of peak positive and negative Doppler velocities with the magnetic
flux growth rate and magnetic field strength for the active regions emerging
near the limb (the horizontal component of plasma flows); iv) of the magnetic
flux growth rate with the density of emerging magnetic flux; v) of the Doppler
velocities and magnetic field parameters for the first hours of the appearance
of active regions with the total unsigned magnetic flux at the maximum of their
development.Comment: 14 pages, 8 figures. The results of article were presented at the
ESPM-13 (12-16 September 2011, Rhodes, Greece, Abstract Book p. 102-103,
P.4.13,
http://astro.academyofathens.gr/espm13/documents/ESPM13_abstract_programme_book.pdf
Photoinduced charge separation in Q1D heterojunction materials: Evidence for electron-hole pair separation in mixed-halide solids
Resonance Raman experiments on doped and photoexcited single crystals of
mixed-halide complexes (=Pt; =Cl,Br) clearly indicate charge
separation: electron polarons preferentially locate on PtBr segments while hole
polarons are trapped within PtCl segments. This polaron selectivity,
potentially very useful for device applications, is demonstrated theoretically
using a discrete, 3/4-filled, two-band, tight-binding, extended Peierls-Hubbard
model. Strong hybridization of the PtCl and PtBr electronic bands is the
driving force for separation.Comment: n LaTeX, figures available by mail from JTG ([email protected]
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