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Radio polarimetric imaging of the solar corona at low frequencies (Record no. 19564)

MARC details
000 -LEADER
fixed length control field 03534nam a2200193Ia 4500
003 - CONTROL NUMBER IDENTIFIER
control field IN-BaIIA
005 - DATE AND TIME OF LATEST TRANSACTION
control field 20211111112446.0
008 - FIXED-LENGTH DATA ELEMENTS--GENERAL INFORMATION
fixed length control field 211028s9999 xx 000 0 eng d
040 ## - CATALOGING SOURCE
Transcribing agency IIA Library
100 ## - MAIN ENTRY--PERSONAL NAME
Personal name Anshu Kumari
9 (RLIN) 37414
Relator term Author
245 #0 - TITLE STATEMENT
Title Radio polarimetric imaging of the solar corona at low frequencies
Remainder of title a thesis submitted for the degree of doctor of philosophy (Technology) in the department of applied optics and photonics, University of Calcutta, Kolkata
Statement of responsibility, etc. Anshu Kumari
Medium [Thesis]
260 ## - PUBLICATION, DISTRIBUTION, ETC.
Place of publication, distribution, etc. Bangalore
Name of publisher, distributor, etc. Indian Institute of Astrophysics
Date of publication, distribution, etc. 2019
300 ## - PHYSICAL DESCRIPTION
Extent xxx, 128p.
500 ## - GENERAL NOTE
General note Ph.D. Thesis, Pondicherry University, Puducherry
502 ## - DISSERTATION NOTE
Degree type Doctor of Philosophy
Name of granting institution University of Calcutta, Kolkata
Year degree granted 2019
520 ## - SUMMARY, ETC.
Summary, etc. The coronal magnetic field (B) plays an important role in the formation, evolution, and dynamics of the small, as well as large scale structures in the solar corona. Measurements of the coronal magnetic field strengths, particularly in the radial distance range ≈ 1.1 - 3.0 R (R is the radius of photospheric Sun) is presently difficult because of practical reasons. Polarization observations, by measuring the Stokes-V parameter of the received radio signal, are generally used as a tool to measure the magnetic field strength associated with the radio emission; the latter is one of the widely pursued areas of research in the solar coronal physics, in addition to the currently available but limited methods of estimating the magnetic field strength using simultaneous radio imaging and spectral observations. Ground based radio observations provide an excellent tool to observe and study the corona in the aforesaid height range. Therefore, the primary objectives of this thesis are to : 1. design, develop and characterize spectro-polarimeter that can receive the polarized radio emission (at low frequencies) from the Sun with high temporal, spectral resolution, etc.; 2. compare the data obtained using the new instruments with the existing instruments in order to improve the observing capabilities of new instruments; 3. estimate the magnetic field strengths from the observed polarized radio emission associated with various forms of solar coronal activities observed at other wavelength parts of the electromagnetic spectrum. As for the first objective is concerned, two spectro-polarimeters were developed : i Near ionospheric cut-off frequency spectro-polarimeter that can operate over 15 - 85 MHz frequency range. ii Wide-band spectro-polarimeter that can operate over 50 - 500 MHz frequency range. For the first spectro-polarimeter system, a Log-Periodic Dipole Antenna (LPDA) that works in the 15 - 85 MHz range was designed and characterized. The VSWR (Voltage Standing Wave Ratio) of the antenna is ≤ 3.0 throughout the band. It has a directional gain of 6 dBi and has an effective collecting area of ≈ 0.3λ 2 . Two identical antennas were fabricated and kept in mutually orthogonal orientations to arrange the frontend. Since the signal strength received by the antennas from the background sky were found to vary drastically over the observing bandwidth it was difficult to handle the entire frequency band with a single digital backend system. Therefore, the signal was split into two sub-bands (15 - 25 MHz & 25 - 85 MHz) using appropriate filters designed as part of the thesis work. The signals were then amplified using Low Noise Amplifier (LNA) and were fed to a digital backened receiver.
700 ## - ADDED ENTRY--PERSONAL NAME
Personal name R. Ramesh
Relator term Supervisor
9 (RLIN) 48864
942 ## - ADDED ENTRY ELEMENTS (KOHA)
Koha item type Thesis & Dissertations
Source of classification or shelving scheme Universal Decimal Classification
Holdings
Withdrawn status Lost status Source of classification or shelving scheme Damaged status Not for loan Home library Current library Shelving location Date acquired Total Checkouts Barcode Date last seen Date last checked out Price effective from Koha item type
    Universal Decimal Classification     IIA Library-Bangalore IIA Library-Bangalore General Stacks 24/08/2021 1 20486 05/09/2022 08/12/2021 24/08/2021 Thesis & Dissertations

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