Looking into something
Those who read the older SAXS literature will note liberal use of Fourier transforms to calculate the scattering behaviour of odd-shaped particles. Likewise, the effects of smearing due to (for example) beam shape (think “blurring” of the scattering pattern) can be easily determined using such transforms. It is useful to get a feel for the methods for derivation of such Fourier transforms, so I decided it was time to refresh my rusty Fourier transform skills.
A little step sideways from small-angle scattering for this week’s post. As you are probably aware by now, I sometimes use the LaN weblog to crystallize ideas into something resembling a coherent story. This is needs to be done now, as I am preparing another presentation (due late January), one that covers a tangential topic from my usual repertoire: a little overview of bad tidings in science. This post is open to read and review on The Winnower.
Last week, I was contacted by Christian Gollwitzer (author of this excellent paper) about something posted here (and in particular detailed in this document) a while ago. It concerns the behaviour of the Guinier approxiation for polydisperse systems, and it looks like I made a mistake when writing that document. This post is open to read and review on The Winnower.
[ed: My current project is running at an end, so if you happen to have a job offer I cannot refuse, I will seriously weigh it against the (tenured) job offer I got from NIMS!] The typical argument in favor of the line-collimated “Kratky”-type instruments is that its X-ray flux is very high and that therefore you need only short measurement times. However, its data needs to be corrected through a “desmearing”-procedure, amplifying uncertainties and noise in the process. Does this approach then really give you better data? Let’s find out! This post is open to read and review on The Winnower.
[ED: I’ve started asking around for guest contributions for the LookingAtNothing site, in order to provide a broader view of the SAS-related activities than I could ever hope to achieve by myself. Our second guest to talk about his work is Dr. Jan Ilavsky of the Argonne National Laboratory.] Maybe you heard my name, Jan Ilavsky, perhaps in association with Ultra-Small Angle Scattering (USAXS) instrument, Irena or Nika software packages, or in relationship with Glassy Carbon absolute intensity standard? We will get to each of these in a few lines, but in order to understand me, you need to understand my history.
[ED: I’ve started asking around for guest contributions for the LookingAtNothing site, in order to provide a broader view of the SAS-related activities that I could ever hope to achieve by myself. Our first guest to talk about his work is Dr. Grégory Stoclet of UMET at the Université Lille 1.] PLA is a new biodegradable polymer used for in many applications such as disposable packaging as medical implants. While it behaves like a brittle material at room temperature, it quickly becomes ductile by raising the temperature a few degrees. To understand why this happens, we are studying the plastic deformation mechanisms using SAXS.
Just a couple of housekeeping notes: I’m giving talks in Europe in a month at the following locations: Unité Matériaux et Transformations (UMET), Lille on May 16, hosted by Grégory Stoclet, Birmingham University, Birmingham on the 20th of May, hosted by Zoe Schnepp, Nottingham University, Nottingham, on the 23rd of May, hosted by Philip Moriarty, Between these dates, I’ll also be joining Zoe and Martin for beamtime at the Diamond synchrotron (beamline I11) between May 21 and May 23. Please feel free to stop me at these locations and say hi! For today, I’ve got another bit of data correction to show. I thought it might be interesting to put them all together and show you what difference it makes to an integrated scattering pattern. Many of the data corrections implemented are quite straightforward shifts and scalings, but some are more involved and have a greater effect on the scattering pattern.
By the way, my topical review paper on SAXS data collection and correction has been published and is available open access here! Recently, some good colleagues (who are not familiar with scattering) have started asking questions on how to go about fitting a scattering pattern. This was a very good opportunity to think about the process from a layman perspective. How do we get from scattering pattern to morphological information in a straightforward way?