Looking At Nothing

capillary self-absorption paper highlight, and new video

2012/01/27 | Author: Brian

Dear scatterers,

Those of you who have been reading this weblog for a while now, may remember the calculation of the sample self-absorption correction for plate-like samples. The result of this was a straightforward equation which could be used to correct the scattering of strongly absorbing samples (>30%) with a plate-like geometry. It was mentioned then, that the calculation of this correction for capillary samples is more complicated, but would be good to have. This sample self-absorption of a capillary will show up as a butterfly-shaped shadow on your scattering pattern.

In the latest issue of J. Appl. Cryst., there is a new paper discussing exactly this. Sulyanov et al. have (programmed) a solution to calculate the sample self-absorption factor for cylindrical samples. The code they provide is available in Fortran, and I will spend some time to try to transcode this into Python in the near future. Judging from their solutions, I am happy I did not try to solve it. The solution seems to be a little bit more complicated than I thought.

Additionally, in the same issue, Zeidler has a solution for samples of spherical geometry. While I have not encountered a problem requiring this solution before, it is certainly noteworthy, and may be of use to some of you doing scattering from suspended objects.

Lastly, there is a new video of one of my latest short presentations online here, explaining a little about my work as well as the monte-carlo analysis method. It’s very short, and there will be a more detailed MC method explanation shortly (as I have promised for quite a while now).

Scatter well!

Presenting for Scientists – video

2012/01/15 | Author: Brian

If you give bad presentations, you can kill people. If you want to find out why, and get some tips on presentation techniques (the ones I use, anyway), you can watch this video I recorded recently.

( http://www.youtube.com/watch?v=eVtL9NCXyEs )

Comments are always welcome!

New video online- presenting observability

2011/12/25 | Author: Brian

Dear readers,

First of all, a merry end-of-year thingie (insert name here) to all of you.

Last week, I presented a short 15-minute talk at the MRS-J conference in Yokohama. While it was a nice opportunity to present and meet people, it is a relatively small conference. With that in mind, I decided to re-record the presentation and post in online so you can take what you want from it. I was slightly ill when re-recording so the edit is a bit choppy (after removing the sneezes).

It is available on Youtube here (and embedded below). Please leave comments and/or thumbs up if you like, and follow me on twitter @drheaddamage if you want to hear more ramblings from this side.

Lastly, the next video definitely should be a custom one explaining the monte-carlo method we’ve developed referred to in the video.

Detail-preserving 2D binning, part 1: the appetizer

2011/12/10 | Author: Brian

(Sorry about the hiatus, there’s been a period filled with that noblest of Japanese traditions: paperwork!)

If you want to do fitting of a 2D image, you want to preserve the information in the entire image. 2D fitting is quite computationally intensive, so you still want to reduce the number of pixels in your images. Methods I have seen published, are occasionally quite poor at preserving detail, but I’ve played with a type of binning (quite similar to the mathematical concept of k-d trees) that does preserve this: Behold the coolness in the following plots, which are different zoom levels of the same scattering pattern. On the vertical axis is the azimuthal angle, on the horizontal axis q (in reciprocal meters). An explanation will follow in the near future, but you’re welcome to write to me for the scoop.

Pretty cool, huh! And since the errors of the intensity of each bin are known, fitting is not affected by the differences in area!

A compact pneumatic fibre tensile stage – publication

2011/11/15 | Author: Brian

It is with pleasure that I can announce the publication of another fibre-related work, right here (The electronic reprint will be made available after December on this site).

This tensile stage was the result of me not wanting to install a massive Instron stage at a beamline, nor did I want to design a vacuum enclosure that would fit around the business end of such a stage. I had a blast designing it and having it built, despite the time constraints imposed by the fast approaching beamtime. I now have the chance to design and build version two of this stage, and I will keep you posted on the progress of that one.

More statistics and change of job

2011/11/04 | Author: Brian

Hello dear readers,

As a followup on my previous story, a colleague of mine sent me this paper that helps explain the standard deviation, standard error and confidence intervals. A useful, and funny read: Click here.

The second noteworthy item is that I have, as of November 1st, started working at the National Institute for Materials Science (NIMS) as a (limited time) independent researcher. From now on, I will be working on a variety of stuff, which revolves around developing anisotropic SAS analysis methodologies. Naturally, I will post items of interest on this site as always, so keep checking in!. Also, don’t hesitate to leave a comment!

Everybody hates statistics…

2011/10/08 | Author: Brian

Everybody hates statistics [1]…

… but it can be of major importance in our small angle world. While very few papers on small-angle scattering discuss statistics, they can tell you whether your observations are real or just imaginary. In addition, statistics will let you know whether you have been able to describe your scattering pattern with your model or not. All in all, nice to have.

I will briefly discuss two statistical concepts which could be of great use, as they have been for me. While I never really could understand all the concepts during statistics lectures at university (a situation which may sound familiar), I can try to explain some simple concepts. By the by, if you (dear reader) are a statistician, I would be happy to get in touch with you. The first concept is the most straightforward, and involves the uncertainties on fitting parameters. Secondly I will discuss statistics on collected intensity and how to retrieve them for a variety of detectors.

Changing jobs…

2011/09/28 | Author: Brian

Dear all,

I will be heading off again into the world of anisotropic scattering after a two-year stint in isotropic scattering. I will be working at NIMS in Tsukuba from November 1st, so if you are in the neighborhood, feel free to stop by for a coffee!

P.S. Sorry for the slow updates, but the administrative business is hardly worth blogging about!

Join the SAS session at the MRS-J conference in Yokohama, Japan! (19-21 December)

2011/09/12 | Author: Brian

There is an upcoming conference in the Japanese city of Yokohama, mere minutes from Tokyo. At that materials research society conference, one particularly fine international session is dedicated to small-angle scattering (SAS). Last year, this SAS session was small but with a good atmosphere and many interesting talks. This year, amongst others, dr. Ilavsky from APS will be giving a talk on data analysis techniques for small-angle scattering. If last year offers grounds for foresight, the session is convivial, the dinner afterwards excellent, and the weather fantastic in a beautiful town (for Japanese standards).

So, If you have the time, do drop by this session, join the talks and share your knowledge! More information and registration opportunities can be found here: http://mrs-j.com/main/?q=en/2011es3&destination=node%2F116

You can also leave a comment or drop me a line if you need more information.

Careful when using Molybdenum radiation sources

2011/08/29 | Author: Brian

Just a quick heads-up. There’s a chance of 0.5% low-energy contamination when using molybdenum or silver radiation sources, even when using focusing devices, according to Macchi et al (doi:10.1107/S0021889811016232). While this is a low contamination level, it may have measurable effects in small-angle scattering of soft, low-absorption samples (simulations may follow soon).

One way of significantly reducing this contamination is by introducing a filter of (~100 micron) aluminium foil, so it should be easy to test whether it affects your experiments or not.