473 research outputs found
Twin Telescope observations of the Sun at Kodaikanal Observatory
We report the design, fabrication and installation of a 'Twin Telescope' at
Kodaikanal Observatory intended to augment the ongoing synoptic observations of
the Sun that has been carried out since 1904. The telescope uses a 15 cm
objective capable of taking Ca-K line filtergrams and photoheliograms in
continuum of the full disk of the Sun simultaneously, at a frequency of 0.1 Hz
using 2kx2k format CCD cameras. The telescope has been in operation since
February 2008 and images are being obtained at a cadence of 5 min during normal
observing periods. In case of solar activity, images of the active regions can
be taken at a frequency of 1 Hz by restricting the field of view and spatial
resolution. In this paper, we describe the telescope, instruments, image
acquisition, data calibration and image processing. We also discussed a method
of determining the network element and plage area index. The preliminary
results show that while the network element covers about 30% of the disk, the
percentage of the network element area index varies marginally with the seeing
conditions during the day.Comment: 17 pages, 10 Figures, to appear in the 2012 March issue of the
Bulletin of the Astronomical Society of Indi
Oscillations in active region fan loops: Observations from EIS/{\it Hinode} and AIA/SDO
Active region fan loops in AR 11076 were studied, in search of oscillations,
using high cadence spectroscopic observations from EIS on board Hinode combined
with imaging sequences from the AIA on board SDO. Spectra from EIS were
analyzed in two spectral windows, \FeXII 195.12 \AA and \FeXIII 202.04 \AA
along with the images from AIA in 171 \AA and 193 \AA channels. We find short
(3 min) and long (9 min) periods at two different locations.
Shorter periods show oscillations in all the three line parameters and the
longer ones only in intensity and Doppler shift but not in line width. Line
profiles at both these locations do not show any visible blue-shifted component
and can be fitted well with a single Gaussian function along with a polynomial
background. Results using co-spatial and co-temporal data from AIA/SDO do not
show any significant peak corresponding to shorter periods, but longer periods
are clearly observed in both 171 \AA and 193 \AA channels. Space-time analysis
in these fan loops using images from AIA/SDO show alternate slanted ridges of
positive slope, indicative of outward propagating disturbances. The apparent
propagation speeds were estimated to be 83.5 1.8 \kms and 100.5 4.2
\kms, respectively, in the 171 \AA and 193 \AA channels. Observed short period
oscillations are suggested to be caused by the simultaneous presence of more
than one MHD mode whereas the long periods are suggested as signatures of slow
magneto-acoustic waves. In case of shorter periods, the amplitude of
oscillation is found to be higher in EIS lines with relatively higher
temperature of formation. Longer periods, when observed from AIA, show a
decrease of amplitude in hotter AIA channels which might indicate damping due
to thermal conduction owing to their acoustic nature.Comment: Accepted for publication in Solar Physic
Preparation of a superabsorbent polymer and exploration of its properties
Natural polymers (from the Greek poly meaning “many” and meros meaning “parts”) are found in many forms such as horns of animals, tortoise shell, shellac (from the lac beetle), rosin (from pine trees), asphalt, and tar from distillation of organic materials. One of the most useful of the natural polymers was rubber, obtained from the sap of the hevea tree. (Rubber was named by the chemist Joseph Priestley who found that a piece of solidified latex gum was good for rubbing out pencil marks on paper. In Great Britain, erasers are still called “rubbers”.) Natural rubber had only limited use as it became brittle in the cold and melted when warmed. In 1839, Charles Goodyear discovered, through a lucky accident, that by heating the latex with sulfur, the properties were changed making the rubber more flexible and temperature stable. That process became known as vulcanization
Relationship between Horizontal Flow Velocity and Cell Lifetime for Supergranulation
A study of 50 supergranular cells obtained from SOHO Dopplergrams was
undertaken in order to investigate the relationship between the lifetime ()
and the horizontal flow velocity () of the cells. For this sample we find
that the two parameters are correlated with a relation and
is identified with the eddy turn-over time. This is in agreement with the
turbulent convective model of the solar atmosphere where the velocity spectrum
of supergranular field given by '' can be identified with
the Kolmogorov spectrum for the eddy size .Comment: 12th International Congress on Plasma Physics, 25-29 October 2004,
Nice (France
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Investigating ontology based query expansion using a probabilistic retrieval model
This research briefly outlines the problems of traditional information retrieval systems and discusses the different approaches to inferring context in document retrieval. By context we mean word disambiguation which is achieved by exploring the generalisation-specialisation hierarchies within a given ontology. Specifically, we examine the use of ontology based query expansion for defining query context. Query expansion can be done in many ways and in this work we consider the use of relevance feedback and pseudo-relevance feedback for query expansion. We examine relevance feedback and pseudo-relevance to ascertain the existence of performance differences between relevance feedback and pseudo-relevance feedback. The information retrieval system used is based on the probabilistic retrieval model and the query expansion method is extended using information from a news domain ontology. The aim of this project is to assess the impact of the use of the ontology on the query expansion results. Our results show that ontology based query expansion has resulted in a higher number of relevant documents being retrieved compared to the standard relevance feedback process. Overall, ontology based query expansion improves recall but does not produce any significant improvements for the precision results. Pseudo-relevance feedback has achieved better results than relevance feedback. We also found that reducing or increasing the relevance feedback parameters (number of terms or number of documents) does not correlate with the results. When comparing the effect of varying the number of terms parameter with the number of documents parameter, the former benefits the pseudo-relevance feedback results but the latter has an additional effect on the relevance feedback results. There are many factors which influence the success of ontology based query expansion. The thesis discusses these factors and gives some guidelines on using ontologies for the purpose of query expansion
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