7,942 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
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
Reasons for female neonaticide in India
Invited commentary on ‘Neonaticide in India and the stigma of female gender: report of two cases’, Mishra et al
The structure of dark matter halos in hierarchical clustering theories
During hierarchical clustering, smaller masses generally collapse earlier
than larger masses and so are denser on the average. The core of a small mass
halo could be dense enough to resist disruption and survive undigested, when it
is incorporated into a bigger object. We explore the possibility that a nested
sequence of undigested cores in the center of the halo, which have survived the
hierarchical, inhomogeneous collapse to form larger and larger objects,
determines the halo structure in the inner regions. For a flat universe with
, scaling arguments then suggest that the core density
profile is, with . But
whether such behaviour obtains depends on detailed dynamics. We first examine
the dynamics using a fluid approach to the self-similar collapse solutions for
the dark matter phase space density, including the effect of velocity
dispersions. We highlight the importance of tangential velocity dispersions to
obtain density profiles shallower than in the core regions. If
tangential velocity dispersions in the core are constrained to be less than the
radial dispersion, a cuspy core density profile shallower than 1/r cannot
obtain, in self-similar collapse. We then briefly look at the profiles of the
outer halos in low density cosmological models where the total halo mass is
convergent. Finally, we analyze a suite of dark halo density and velocity
dispersion profiles obtained in cosmological N-body simulations of models with
n= 0, -1 and -2. We find that the core-density profiles of dark halos, show
considerable scatter in their properties, but nevertheless do appear to reflect
a memory of the initial power spectrum, with steeper initial spectra producing
flatter core profiles. (Abridged)Comment: 31 pages, 7 figures, submitted to Ap
Numerical control of laser processing and simulation of microstructures and temperature profiles - a fuzzy approach
The use of high power density laser beam for surface modification of many important alloys often leads to appreciable changes in the composition & tribological properties. These changes are dependent on process variables such as beam size, energy, scan rate, laser
mode and the Chemistry and metallurgy of steel. Appro-ximate solutions to heat flow equations are combined
with kinetic models to predict the microstructures and temperature distributions. A transient fuzzy logic
based heat flow model is developed to predict temperature
zones instead of discrete temperature calculations. A set of separate membership functions are formulated for dete-rmining temperature zones by means of continuous iteration process the same method is adopted to evaluate micro-structures for a specific temperature zone by incorporat-ing the kinetic and thermal datas available. Alloy steel of CK45 grade and stainless steel of 316 grade are used for this investigations and the results obtained are compared with the temperature profiles obtained from conventional methods and hence their microstructures. An attempt is also made to compute the dendrite cell width distribution during laser melt solidification of 316 LN steel by means of the above mentioned method
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