608 research outputs found
Multiwavelength Study on Solar and Interplanetary Origins of the Strongest Geomagnetic Storm of Solar Cycle 23
We study the solar sources of an intense geomagnetic storm of solar cycle 23
that occurred on 20 November 2003, based on ground- and space-based
multiwavelength observations. The coronal mass ejections (CMEs) responsible for
the above geomagnetic storm originated from the super-active region NOAA 10501.
We investigate the H-alpha observations of the flare events made with a 15 cm
solar tower telescope at ARIES, Nainital, India. The propagation
characteristics of the CMEs have been derived from the three-dimensional images
of the solar wind (i.e., density and speed) obtained from the interplanetary
scintillation data, supplemented with other ground- and space-based
measurements. The TRACE, SXI and H-alpha observations revealed two successive
ejections (of speeds ~350 and ~100 km/s), originating from the same filament
channel, which were associated with two high speed CMEs (~1223 and ~1660 km/s,
respectively). These two ejections generated propagating fast shock waves
(i.e., fast drifting type II radio bursts) in the corona. The interaction of
these CMEs along the Sun-Earth line has led to the severity of the storm.
According to our investigation, the interplanetary medium consisted of two
merging magnetic clouds (MCs) that preserved their identity during their
propagation. These magnetic clouds made the interplanetary magnetic field (IMF)
southward for a long time, which reconnected with the geomagnetic field,
resulting the super-storm (Dst_peak=-472 nT) on the Earth.Comment: 24 pages, 16 figures, Accepted for publication in Solar Physic
Usporedna analiza sekvenci dijagnostičkih PCR umnožaka virusa ovčjih boginja iz indijske ovce
Field samples were identified by agar gel precipitation and polymerase chain reaction (PCR) as positive for sheeppox virus. Envelope protein gene PCR amplicons (192 bp) of Indian sheeppox viruses isolated in 1997 and 2003 were sequenced to analyse nucleotide divergence. Analysis revealed that 2003 isolates possessed 100% nucleotide identity to each other, but only 95% nucleotide and amino acid were identity to an isolate from 1997. These Indian isolates were unique from other capripox virus sequences in that they contained a single codon insertion. Consistent with previous findings, the results indicate that recent sheepox virus isolates in India are more similar to previously described sheepox virus than to goatpox viruses from India and elsewhere.Virus ovčjih boginja dokazan je u terenskim uzorcima imunodifuzijom u gelu i lančanom reakcijom polimeraze (PCR). PCR umnošci gena za protein ovojnice (192 pb) indijskih izolata virusa ovčjih boginja izdvojenih tijekom 1997. i 2003. razlikovali su se po nukleotidnom slijedu. Izolati iz 2003. međusobno su bili identični u 100% nukleotida, dok je izolat iz 1997. bio njima podudaran samo u 95% nukleotida i aminokiselina. Ti indijski izolati bili su jedinstveni u odnosu na druge viruse boginja koza po jednom ugrađenom kodonu. U skladu s prijašnjim istraživanjima, nalazi ukazuju da su nedavni izolati virusa ovčjih boginja u Indiji sličniji ranije opisanim virusima ovčjih boginja nego virusima kozjih boginja iz Indije i drugdje
Neel state of antiferromagnet as a result of a local measurement in the distributed quantum system
Single-site measurement in a distributed macroscopic antiferromagnet is
considered; we show that it can create antiferromagnetic sublattices at
macroscopic scale. We demonstrate that the result of measurement depends on the
symmetry of the ground state: for the easy-axis case the Neel state is formed,
while for the easy-plane case unusual ``fan'' sublattices appear with unbroken
rotational symmetry, and a decoherence wave is generated. For the latter case,
a macroscopically large number of measurements is needed to pin down the
orientation of the sublattices, in spite of the high degeneracy of the ground
state. We note that the type of the final state and the appearance of the
decoherence wave are governed by the degree of entanglement of spins in the
system.Comment: 4 REVTeX pages, 1 figure in PostScrip
Multi-wavelength Diagnostics of the Precursor and Main phases of an M1.8 Flare on 2011 April 22
We study the temporal, spatial and spectral evolution of the M1.8 flare,
which occurred in NOAA AR 11195 (S17E31) on 22 April 2011, and explore the
underlying physical processes during the precursors and their relation to the
main phase. The study of the source morphology using the composite images in
131 {\deg}A wavelength observed by the SDO/AIA and 6-14 keV revealed a
multiloop system that destabilized systematically during the precursor and main
phases. In contrast, HXR emission (20-50 keV) was absent during the precursor
phase, appearing only from the onset of the impulsive phase in the form of
foot-points of emitting loop/s. This study has also revealed the heated
loop-top prior to the loop emission, although no accompanying foot-point
sources were observed during the precursor phase. We estimate the flare plasma
parameters viz. T, EM, power-law index, and photon turn-over energy by forward
fitting RHESSI spectral observations. The energy released in the precursor
phase was thermal and constituted ~1 per cent of the total energy released
during the flare. The study of morphological evolution of the filament in
conjunction with synthesized T and EM maps has been carried out which reveals
(a) Partial filament eruption prior to the onset of the precursor emission, (b)
Heated dense plasma over the polarity inversion line and in the vicinity of the
slowly rising filament during the precursor phase. Based on the implications
from multi-wavelength observations, we propose a scheme to unify the energy
release during the precursor and main phase emissions in which, the precursor
phase emission has been originated via conduction front formed due to the
partial filament eruption. Next, the heated leftover S-shaped filament has
undergone slow rise and heating due to magnetic reconnection and finally
erupted to produce emission during the impulsive and gradual phases.Comment: 16 Pages, 11 Figures, Accepted for Publication in MNRAS Main Journa
Simple model for scanning tunneling spectroscopy of noble metal surfaces with adsorbed Kondo impurities
A simple model is introduced to describe conductance measurements between a
scanning tunneling microscope (STM) tip and a noble metal surface with adsorbed
transition metal atoms which display the Kondo effect. The model assumes a
realistic parameterization of the potential created by the surface and a
d3z2-r2 orbital for the description of the adsorbate. Fano lineshapes
associated with the Kondo resonance are found to be sensitive to details of the
adsorbate-substrate interaction. For instance, bringing the adsorbate closer to
the surface leads to more asymmetric lineshapes while their dependence on the
tip distance is weak. We find that it is important to use a realistic surface
potential, to properly include the tunnelling matrix elements to the tip and to
use substrate states which are orthogonal to the adsorbate and tip states. An
application of our model to Co adsorbed on Cu explains the difference in the
lineshapes observed between Cu(100) and Cu(111) surfaces.Comment: 11 pages, 8 eps figure
STM conductance of Kondo impurities on open and structured surfaces
We study the scanning tunneling microscopy response for magnetic atoms on
open and structured surfaces using Wilson's renormalization group. We observe
Fano resonances associated with Kondo resonances and interference effects. For
a magnetic atom in a quantum corral coupled to the confined surface states, and
experimentally relevant parameters, we observe a large confinement induced
effect not present in the experiments. These results suggest that the Kondo
screening is dominated by the bulk electrons rather than the surface ones.Comment: 6 pages, 6 figure
Long-range Kondo signature of a single magnetic impurity
The Kondo effect, one of the oldest correlation phenomena known in condensed
matter physics, has regained attention due to scanning tunneling spectroscopy
(STS) experiments performed on single magnetic impurities. Despite the
sub-nanometer resolution capability of local probe techniques one of the
fundamental aspects of Kondo physics, its spatial extension, is still subject
to discussion. Up to now all STS studies on single adsorbed atoms have shown
that observable Kondo features rapidly vanish with increasing distance from the
impurity. Here we report on a hitherto unobserved long range Kondo signature
for single magnetic atoms of Fe and Co buried under a Cu(100) surface. We
present a theoretical interpretation of the measured signatures using a
combined approach of band structure and many-body numerical renormalization
group (NRG) calculations. These are in excellent agreement with the rich
spatially and spectroscopically resolved experimental data.Comment: 7 pages, 3 figures + 8 pages supplementary material; Nature Physics
(Jan 2011 - advanced online publication
North-South Distribution of Solar Flares during Cycle 23
In this paper, we investigate the spatial distribution of solar flares in the
northern and southern hemisphere of the Sun that occurred during the period
1996 to 2003. This period of investigation includes the ascending phase, the
maximum and part of descending phase of solar cycle 23. It is revealed that the
flare activity during this cycle is low compared to previous solar cycle,
indicating the violation of Gnevyshev-Ohl rule. The distribution of flares with
respect to heliographic latitudes shows a significant asymmetry between
northern and southern hemisphere which is maximum during the minimum phase of
the solar cycle. The present study indicates that the activity dominates the
northern hemisphere in general during the rising phase of the cycle
(1997-2000). The dominance of northern hemisphere is shifted towards the
southern hemisphere after the solar maximum in 2000 and remained there in the
successive years. Although the annual variations in the asymmetry time series
during cycle 23 are quite different from cycle 22, they are comparable to cycle
21.Comment: 6 pages, 2 figures, 1 table; Accepted for the publication in the
proceedings of international solar workshop held at ARIES, Nainital, India on
"Transient Phenomena on the Sun and Interplanetary Medium" in a special issue
of "Journal of Astrophysics and Astronomy (JAA)
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