This blog is moving

This blog is now being integrated into my main web-pages and is
therefore moving to the following address

http://www.mrao.cam.ac.uk/~bn204/blog/

All of the articles have been transferred there and all new posts will
go there only. Thanks for reading and please update your Atom/RSS
readers!

Astrophysical techniques graduate course

I've just finished lecturing the astrophysical techniques course -- if
anybody is interested all of the slides are available here:

http://www.mrao.cam.ac.uk/~bn204/lecture/astrotechniques.html

Atmospheric Phase Correction for ALMA & The WVRGCAL program

The slides of this talk that I gave at the NRAO ALMA Software
Development Workshop are available here:

http://www.mrao.cam.ac.uk/~bn204/publications/2011/2011-October-Charlottesville.pdf

A Better Interface Between Scientists and Data Reduction Software

This is a talk that I have at the NRAO ALMA Software Development
workshop
(https://science.nrao.edu/facilities/alma/naasc-workshops/almasoft2011/index). The
slides are here:

http://www.mrao.cam.ac.uk/~bn204/publications/2011/2011-10-cv-workshop-slides.pdf

And this is the abstract

I this talk I will argue that, although it has much improved in recent
years, the typical way we interact with data reduction software (that
is, the software that turns the bulky observed measurements into a
smaller data set of images, spectra, etc, that is then further
interpreted) is still not ideal. Some particularly important
shortcomings are:

- Operations on data are performed only ever strictly in the sequence
supplied by the user (either interactively or through
functions/scripts)

- Commands available to the user often combine instructions about what
needs to be done with the details of how this is done

- Information on (potential) problems in the data is difficult to
share across different observations

The consequences of these apparently simple shortcomings are that data
reduction is much more labour and computer intensive than it needs to
be. Since with ALMA, EVLA and forthcoming SKA precursors we are
likely to be short both of available labour and computing power, I
suggest that investing in better interfaces is essential.

In the second part of this talk I will present a set of straw-man
requirements for a better interface between scientists and data
reduction software and show how these requirements would resolve the
shortcomings listed above. I will discuss a possible way of
implementing these and show that such a system can easily build on top
of existing data reduction systems such as CASA. I will argue that the
three benefits of such a system would be:

- Increasing the quantity of science from each scientist and kWh of
compute power by improving their efficiency

- Improving the quality of science by easing repeatability and
reducing scope for error

- Making it easier for user scientists to send instructions to the
observatory on how their data needs to be reduced -- an essential
feature for forthcoming telescopes with extremely high data rates

Atmospheric Phase Correction for ALMA with 183 GHz Water Vapour Radiometers -- URSI GA 2011 paper

The PDF of the paper is available here:

http://www.mrao.cam.ac.uk/~bn204/publications/2011/nikolicga11.pdf

The PDF of the slides of the presentation at the conference:

http://www.mrao.cam.ac.uk/~bn204/publications/2011/nikolicwvr11.pdf

Abstract:

One of the great challenges for ALMA is overcoming the natural limits set by the turbulence in the atmosphere to achieve resolutions as fine as ten milli-arcseconds. A critical component in the strategy to achieve this are mm-wave radiometers on each of the 12m diameter telescopes that observe the emission from the atmospheric water vapour line at 183GHz. The information from these radiometers can be used to compute the fluctuations in total water vapour along the line of sight of each telescope, and from this, the fluctuation in effective path to each antenna. The estimates of path fluctuations are then used to phase-rotate recorded visibilities leading to much increased coherence. In this paper we briefly review the design of the radiometers, describe the software processing steps to derive phase corrections and show some of the first results from the ALMA site in Chile.

ESO Messenger article on tests of radiometric phase correction at ALMA

The PDF is available at:

http://www.mrao.cam.ac.uk/~bn204/publications/2011/messenger-no143-11-15.pdf

Talk at the University of Cambridge

I gave the following talk here at the University of Cambridge:

Abstract:

Observed broad-band radio spectra of both galactic and extra-galactic
objects contain valuable information about their energetics, dynamics
and the physical processes involved in the radio emission. Extracting
this information is however complicated by the fact that there are often
several alternative models for the radio emission; and, by the many
parameters in these models which are only approximately a-priori
constrained.

I will describe a computer program for straightforward Bayesian analysis
of radio spectra based on the nested sampling algorithm. Such an
analysis provides for objective model selection, easy handling of
nuisance parameters, and of course a natural way to handle a-priori
constraints on parameters. I will show some example analyses: a
supernova remnant, a star-forming region in a near-by spiral, and a
number of nearby (U)LIRGs.

PDF: http://www.mrao.cam.ac.uk/~bn204/publications/2010/2010-11-02-Cambridge.pdf