Under Construction !
My research and study interests include computational physics, numerical math and high
performance computing, applied to techniques in radio interferometry.
Monte-Carlo Image analysis in Radio Interferometry, Urvashi R.V.,
T.J.Cornwell, Astronomical Data Analysis Software and Systems XIV
ASP Conference Series,Vol. xxx,p-xxx, 2004 [ps / pdf].
Automatic RFI identification and flagging, Urvashi R.V., Rao, A. Pramesh,
NCRA Technical Report No. R00202, October 1 2003
[ps / pdf].
Solving for Polarization Leakage
in Radio Interferometers Using Unpolarized Sources, Bhatnagar S.,
Urvashi R.V., Nityananda R.,Astronomical Data
Analysis Software and Systems XII ASP Conference Series, Vol. 295, p-469, 2003
[ps / pdf].
A performance model and load balancer for a Parallel Monte-Carlo
Cellular microphysiology simulator, Urvashi R.V., MS thesis,
Department of Computer Science and Engineering, University of California,
San Diego, June 2004. [html /
ps / pdf].
NRAO,Socorro, (July 2005 - present)
Algorithms currently in use for multi frequency synthesis imaging assume that
source fluxes are either constant across the total bandwidth being imaged or
follow a power law (log linear). Moreover, existing multi frequency
synthesis algorithms were designed to optimize on spatial frequency coverage
and are limited to upto 25% bandwidths. EVLA bandwidths range up to 50%
and source structure (flux density) is known to be non constant/power-law
across the total band.
The first part of this project involves simulating data as per EVLA
specifications, and testing existing algorithms with regard to the achievable
dynamic range, sensitivity and image fidelity. The second part is to
extend the Conway-Sault algorithm to account for varying spectral index
across the band (log-quadratic / turnover featues), as well as adopting a multi-scale approach.
Monte Carlo image analysis in radio interferometry
NRAO,Socorro (June 2004 - September 2004)
Image analysis, such as component fitting of radio interferometric images has
traditionally been based on likelihood techniques applied to deconvolved images.
The analysis usually ignores uncertainties arising from fitting overlapping
components to extended emission as well as from the process of deconvolution
itself. This project involved the design and implementation of a Bayesian
approach to image reconstruction in radio interferometry, based on Markov Chain
Monte Carlo techniques. An ensemble of parameter sets was gathered from the
appropriate posterior distribution and used to estimate the relative
probabilities and uncertainties associated with the number of elliptical
gaussian components and their parameters.
Dynamic load balancing for MCell-K
[html / ps / pdf].
CSE, UCSD (Sept 2003 - June 2004)
This thesis presents a performance model for a parallel cellular
microphysiology simulator and discusses dynamic load balancing techniques
that employ it. A hybrid performance model was derived and then tuned to
accurately estimate and predict the characteristics of each simulation.
Workload estimates obtained with the hybrid model were used to drive a
partitioner that adaptively partitioned the workload and improved the
parallel runtime performance by a factor of two on 16 processors.
Operating System Performance Measurements on Redhat Linux 8.0 and Windows
CSE-221 course project, CSE, UCSD (Jan 2003 - March 2003)
This project involved designing and testing a set of metrics to measure and
compare the performance of Redhat Linux 8.0 and Windows XP 5.1, installed on
the same hardware. Metrics which measured memory/disk bandwidths and process
statistics were used to highlight the way each operating system manipulates
the hardware, given different implementation strategies for an application code.
These observations when analysed in terms of efficient software design, can be
used to design algorithms that use the behaviour of the operating system to its
advantage, or equivalently, to take measures to avoid common pitfalls.
CSE, UCSD (Sept 2002 Dec 2002)
Gridding in Radio Astronomical Data Analysis involves transferring irregularly
spaced data onto a regular grid. Given high data rates and the frequency of
performing this operation, it appears as a bottleneck in the entire data
processing pipeline. The irregular nature of the data, as well as different
data ordering requirements, makes straightforward data parallelization result
in non-optimal throughput. This project involved a simple parallel KeLP
implementation, along with a discussion of a few strategies based on locality,
to improve efficiency.
(PSII) Automatic RFI Identification and Flagging
[ps / pdf]
NCRA, TIFR (Jan 2002 - June 2002)
involved the design and implementation of an automatic RFI identification and
flagging algorithm for radio interferometric data sets. The algorithm is based
on a pattern recognition technique customized to typical RFI characteristics
and applied based on autocorrelation data recorded at each antenna.
The current version of this algorithm has been released as a part of
offline software distribution.
Autoflag tool for AIPS++ AOC, NRAO (August 2002)
During the summer of 2003, I spent four weeks at the AOC, NRAO, Socorro,
implementing the RFI flagging algorithm into AIPS++
as an autoflag agent. It was partially integrated into the framework of the
AIPS++ autoflag tool and its working was demonstrated through a glish script.
(PSII) Numerical Solutions for Complex Antenna Gains - Algorithms and Simulations
[ps] and [txt]
NCRA, TIFR (Jan 2002 - June 2002)
The computation of complex antenna gains as a part of instrument calibration in
radio interferometry can be seen as a non-linear least squares problem and is
usually solved by an iterative steepest descent algorithm. This project involved
implementations using three other numerical methods - (1)Levenberg-Marquardt
Newton Raphson (2) Solution by Singular Value Decomposition, and (3) Linearizing via
logarithms. The first two algorithms were extended to solve for additional
terms in the model, to estimate polarization leakages between the
cross-polar feeds mounted on each antenna. A pure simulation
of a full-stokes gain and leakage solver was also developed on the same lines.
(A note written by R.Nityananda : [ps]).
Basics of Signal Processing and Radio Astronomy -
Construction of a dipole antenna to detect the Jovian decametric
BITS, Pilani (Aug 1999 - May 2000)
This Lab Oriented Project focussed on the basics of radio astronomy, antenna
theory, super-heterodyne receiver systems and related basic signal processing.
It involved the construction a simple antenna/receiver system, to detect and
observe the decametric radio emission from the Jupiter-Io interaction. The
setup involved a 6.8m long dipole connected via a co-axial cable to a radio
receiver, tuned to a reception frequency of between 18 and 23 MHz. A cathode
ray oscilloscope was connected across the speaker terminals of the radio, to
observe wave patterns in the kilohertz range. It was found that there was a
roughly periodic, rising and falling hiss at approximately 22MHz, over the
background noise, when Jupiter was in the visible hemisphere of the sky.
The times at which these patterns were observed, roughly coincided with
Jovian radio noise predictions, obtained from
Image Reconstruction via Fourier methods (Computer Aided Tomography),
BITS, Pilani (Aug 2000 - Dec 2000)
Comparative Study of Algebraic Deconvolution Algorithms
NCRA,TIFR (May 2001 - June 2001)
Wavelet Theory and Image Compression,
BITS,Pilani (Jan 2001 - May 2001)
Fragile Watermarking for data authentication,
CS APOGEE 2001, BITS, Pilani (March 2001)
Code Optimization of an e-book reader prototype on the DSC21 ,
Texas Instruments, Bangalore, India (July 2001 - Dec 2001)
Essentials of CNC programming on the LMV-Junior,
Lakshmi Machine Works(LMW),Coimbatore,India (June 1999 - July 1999)