http://hdl.handle.net/2248/5837 Search the Channel search http://prints.iiap.res.in/simple-search http://hdl.handle.net/2248/5841 Title: Extraction of Solid State Features of Carbon Dust Grains in the ISM, from X-Ray Absorption Studies<br/><br/>Authors: Manpreet Singh<br/><br/>Abstract: The subject of dust formation in space is important in diverse environments. The formation of dust proceeds towards the formation of stellar objects and planets. So, it becomes very important for us to know the composition and structure of the dust in order to understand the above mentioned complex systems.Carbon grains are considered for long to be very important candidates for the dust in the interstellar medium (ISM). Existence of carbon in graphite form in the ISM, is an unsolved problem. The present approach will provide a probe, complimentary to the existing ones. It involves extraction of solid state features of carbon dust grains in the ISM, from x-ray absorption studies.A general theory of X-Ray Absorption Fine Structure (XAFS) will be presented. An approximate evaluation of this theory is proposed which allows us to predict the structure of the constituents of the grain. Some case studies are presented for various configurations of graphite and diamond.<br/><br/>Description: Thesis Supervisors: Prof. S Chatterjee & Prof. H C Bhatt Sat, 29 May 2010 22:58:59 GMT http://hdl.handle.net/2248/5838 Title: Helicity Constrained Model of a Galactic Dynamo<br/><br/>Authors: Avijeet Prasad<br/><br/>Abstract: Magnetic fields correlated on kiloparsec scales are seen in disc galaxies. The origin could be dueto amplification of small scale seed fields by a turbulent dynamo. Helicity conservation imposesconstraints on dynamo action and one can study the minimal field strength of the large scale magneticfield that could arise despite the constraint. The calculation of helicity is technically complicatedbecause of open boundaries and the usual form for the MHD invariant needs to be modified to takethis into account. A general formalism has been developed to calculate the field strength using aquasi-linear dynamo model. As a first step, a galactic disk dynamo model has been built analyticallywhile making the usual assumptions of shear and the alpha effect. We find quadrupolar solutions that arematched to a vacuum field with D = 11. The general approach to solving the quasi-linear dynamousing the full set of relative helicity boundary conditions are described<br/><br/>Description: Thesis Supervisor Prof. Arun Mangalam; Restricted Access Sat, 29 May 2010 22:58:59 GMT