Research
Main Teaching Research About
Brock University : Physics Department : Thad Harroun  
Maple leaf with neutrons
Membrane biophysics

My interest is on the structural and physical characteristics of membranes and membrane proteins. Below you will find interesting links related to my research.

My work is supported in large part by the National Sciences and Engineering Research Council of Canada, and most of my experiments are carried out at the Canadian Neutron Beam Centre. I also serve on the Board of Directors for the Candian Institute for Neutron Scattering.

Students

Michelle Przedborski (PhD 2017)

Brad Van Oosten (PhD 2016)

Drew Marquardt (PhD 2014)

Feryaal A.(BSc 2016)

Jill E.(BSc 2014)
Panteha Razavi (MSc 2009)
Some Interests

Explore the various mesophases formed by "bicelle" mixtures of long and short chain lipids.

A structural study of the myristoylated peptide from the N-terminus of ARF-1.

The relocation of cholesterol in poly-unsaturated lipid membranes.

CV and Publications
Data analysis software
 
I have, for some time, the goal to analyse reflectometry data on soft materials, where the surface roughness is quite high, and the layers are thin or inhomogeneous, and the data may incorporate multiple contrasts. There are many suggestions in the literature for how to analyse these types of data, but software is highly limited in availability or generality. Updated May 2008
Yanera (Yet Another NEutron Reflectivity Analyzer) is a program that can be very broadly used for simulation and fitting of neutron and x-ray reflectivity data. Any number data sets can be fit simultaneously, using a variety of models. The link to the right leads to documentation and download for a fairly extensive, stable, and easy to use implementation of Parratt's method. Some features:
  • Simulates or fits neutron reflectometry data using the Parratt formalism.
  • It can simultaneously fit several data sets. This can be useful:
    • For multiple contrast conditions, e.g. the sample was measured in different D2O concentrations. It is now possible to fit all contrast conditions at the same time, using shared parameters for the underlying layers that are not changing their scattering length density.
    • For changing samples, e.g. if a layer was added or removed in situ, and the underlying structure was unaltered.
    • For polarized neutron reflectometry, e.g. fit both spin-up, spin-down, and unpolarized, all at the same time, since the only difference is the application of the magnetic scattering length density.
  • Specify layers in different ways:
    • Homogeneous slabs with gaussian roughness. This is like the Parratt formalism.
    • Functional components made of a sum of Gaussian and Box functions. Construct many novel scattering length density profiles from these components, which can share parameters.
    • A user supplied functional expression. Any inhomogeneous slab layer can have a user-supplied expression to represent its scattering length density, e.g.. a*exp(-(x-21.2)/c), where a and c are fitting parameters
  • It can fit data using several different algorithms provided by the GNU Scientific Library.
  • Use arbitrary instrumental resolution smearing.
  • Written in ANSI-C. Developed under GNU/Linux, a binary version is available on Windows XP.
  • Command line only, no user interface (yet), but input and output are through an very easy to read XML file.
yanera
Updates: April, 2008
The original program yanera is based on is here. Development has stopped for it. Parratt
With this link, you can view a generic framework for using the Gnu Scientific Library for fitting data. It is designed to use mulitple fitting functions that do not have analytical derivatives. The framework is very general, and it allows the choice of least squares, multidimensional minimization, as well as simulated annealing. Fitting data with the GSL