12,511 research outputs found
Source Regions of Coronal Mass Ejections
Observations of the solar corona with the Large Angle Spectrometric
Coronograph (LASCO) and Extreme ultraviolet Imaging Telescope (EIT) instruments
on the Solar and Heliospheric Observatory (SOHO) provide an unprecedented
opportunity to study coronal mass ejections (CMEs) from their initiation
through their evolution out to 30 \rsun. The objective of this study is to gain
an understanding of the source regions from which the CMEs emanate. To this
end, we have developed a list of 32 CMEs whose source regions are located on
the solar disk and are well observed in EIT 195 {\AA} data during the period
from so lar minimum in January 1996 through the rising part of the cycle in May
1998. We compare the EIT source regions with photospheric magnetograms from the
Michelson Doppler Imager (MDI) instrument on SOHO and the NSO/Kitt Peak
Observatory and also with H data from various sources. The overall
results of our study show that 41% of the CME related transients observed are
associated with active regions and have no prominence eruptions, 44% are
associated with eruptions of prominences embedded in active regions and 15% are
associated with eruptions of prominences outside active regions. Those CMEs
that do not involve prominence eruptions originate in active regions both with
and without prominences. We describe 6 especially well observed events. These
case studies suggest that active region CMEs (without eruptive prominences) are
associated with active regions with lifetimes between 11--80 days. They are
also often associated with small scale emerging or cancelling flux over
timescales of 6--7 hours. CMEs associated with active region prominence
eruptions, on the other hand, are typically associated with old active regions
with lifetimes 6-7 months.Comment: Accepted for publication in ApJ, scheduled for Nov 1, 2001 issu
Small electron acceleration episodes in the solar corona
We study the energetics of nonthermal electrons produced in small
acceleration episodes in the solar corona. We carried out an extensive survey
spanning 2004--2015 and shortlisted 6 impulsive electron events detected at 1
AU that was not associated with large solar flares(GOES soft X-ray class
C1) or with coronal mass ejections. Each of these events had weak, but
detectable hard Xray (HXR) emission near the west limb, and were associated
with interplanetary type III bursts. In some respects, these events seem like
weak counterparts of "cold/tenuous" flares. The energy carried by the HXR
producing electron population was -- erg, while
that in the corresponding population detected at 1 AU was -- erg. The number of electrons that escape the coronal
acceleration site and reach 1 AU constitute 6 % to 148 % of those that
precipitate downwards to produce thick target HXR emission
Nucleophilicity/Electrophilicity Excess in Analyzing Molecular Electronics
Intramolecular electron transfer capability of all metal aromatic and
anti-aromatic aluminum cluster compounds is studied in terms of density
functional theory based global and local reactivity descriptors. This study
will provide important inputs towards the fabrication of the material required
for molecular electronics.Comment: 21 pages, 6 figures, 13 table
GM crops and gender issues
Correspondence in the December issue by Jonathan Gressel not only states that gender issues in rural settings have not been adequately addressed with respect to weed control biotech but also asserts that such technology can increase the quality of life of rural women in developing countries. Improved weed control is a labor-saving technology that can result in less employment in a labor surplus rural economy. Often in rural areas, wage income is the main source of income and an important determinant of the quality of life, particularly where employment opportunities are generally limited. Apart from soil preparation, planting and weeding, harvesting is also 'femanual' work that can generate more employment if yields are higher. Biotech can enhance the quality of life of women but only if the technology is associated with overall generation of rural employment
AdS (In)stability: Lessons From The Scalar Field
We argued in arXiv:1408.0624 that the quartic scalar field in AdS has
features that could be instructive for answering the gravitational stability
question of AdS. Indeed, the conserved charges identified there have recently
been observed in the full gravity theory as well. In this paper, we continue
our investigation of the scalar field in AdS and provide evidence that in the
Two-Time Formalism (TTF), even for initial conditions that are far from
quasi-periodicity, the energy in the higher modes at late times is
exponentially suppressed in the mode number. Based on this and some related
observations, we argue that there is no thermalization in the scalar TTF model
within time-scales that go as , where measures
the initial amplitude (with only low-lying modes excited). It is tempting to
speculate that the result holds also for AdS collapse.Comment: 10 pages, 4 figure
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