A while ago I posted the raytraced design of a liquid sample holder that doubled as an oven. Here’s the picture of the final product, and I’ve been told it can even hold water (although solvents with a lower viscosity do leak through).  For those not familiar with this design, it contains a small amount of liquid between two thin mica plates separated by an o-ring. The thickness of the o-ring determines the pathlength. This was designed so that even for a small pathlength (i.e. 0.5 mm), an X-Ray beam with 1mm diameter could be used. At the bottom of the picture, an o-ring is visible, as well as two screws to tighten the device, and one piece of plastic intended for torque removal upon tightening (so that the windows are not affected by torque). The device goes up to 250 degrees when heat probes and a thermocouple are inserted.

Herewith a small program I wrote a while ago and some documentation on how it’s built up.

The Matlab program can calculate the scattering pattern of a superellips of revolution. I hope it is of some use to some of you, if only for satisfying curiosity. The program runs in Matlab, opens a GUI, which requires the input of five variables.

The first two dictate the limits in q that one is interested in. The minimum q value determines the maximum size of the real-space box, and the distance between the minimum q and the maximum q determines the pixel resolution in real space. Good values for these are, for example, 0.01 for the minimum q and 2 for the maximum q. 

The three other variables determine the size and shape of the superellips-of-revolution. The superellips is generated  with width a (in Angstrom), height b, and curvature r. The ellips is then revolved around the vertical axis to generate the ellips-of-revolution. A nice value for these are, for example, a=20, b=100, r=4. 

Please see the attached documentation and have fun running the program. The program is distributed under the GPL V3 license. geomsuperell.pdfsuperellips-of-revolution scattering pattern simulator 

I’ve borrowed a copy of the book “X-Ray Scattering of Soft Matter” by Norbert Stribeck (published by Springer) from one of my supervisors, and I’ve taken some time to browse through it. I must admit, I haven’t read it cover-to-cover, but have tried to use it as a reference book, just like ye olde “Small Angle X-Ray Scattering” from Glatter and Kratky (Online available as PDF here: Small Angle X-ray Scattering).   

The author is well-known in the field of fibre scattering, having studied under prof Ruland. This book, then, contains may references and useful information for samples with fibre symmetry. I’ve used this book in that sense as a sort of review article, since it necessarily also references to quite a few articles concerning my particular topic. In that sense, this book provides a good set of pointers for researchers working on fibres.  

The  book, in my opinion, has a scope that is a little too broad. To give you an impression: there are chapters on polymer physics, X-Ray basics, experimental systems, proposal writing guides, tips and hints for getting most out of beamtime, data analysis, orientation effects and data fitting techniques. This can be a good thing, but it seems that the broadness has affected the depth of the material included, that is to say, I think too little is said on each topic. One prime example of the brevity is the section on when the Guinier approximation can be used for extrapolation of the scattering pattern to q=0. The section 8.1.2 (which discusses this) can be quoted in its entirity: 

“Without any interpretation, Guinier’s law can be used to extrapolate small-angle data towards zero scattering angle, if the measured data cover a part of the Guinier region, i.e. where Eq (8.1) or Eq (8.2) is valid.”

Equation 8.1 and 8.2 are different forms of the Guinier approximation. So essentially, this section states that the Guinier approximation can be used if it is valid, which doesn’t answer my questions on the application of the Guinier method for systems where it clearly cannot be valid (a dense system of polydisperse, anisotropic, particles with a high aspect ratio).   

That said, the tips and hints given in this book stem from the many years of experience that Stribeck has behind his belt. This makes the book a worthwile read (esp. regarding the sections on beamtime hints and tips, for example). In other areas, the book provides a good overview and concatenation of the (sometimes sketchy) articles of the past. One item to which this applies is the “Ruland Streak Method” which nicely exposes the details in an easily understood manner. 

One minor gripe that I think deserves some attention, nonetheless, is the relatively poor quality of some of the images. Whilst much attention has been given to the text, equations and diagrams, there are examples of “home-made” pictures in the book (e.g. Fig 10.1 and 9.1) which simply do not belong in a high-quality book like this and degrade its overall appearance. Some figures (e.g. Fig 9.9) also lack some explanatory qualities, and are difficult to understand. 

All in all, the book is a good reference, but contains some rough edges and is certainly not the final word on each topic in the book. I’d like to see a next edition which elaborates a little more on each topic, with slightly more attention to the figures and pictures. Some chapters go too deep too fast, whilst others merely graze the surface of each topic without going deep enough. Still, it’s a good read and contains many worthwile sections, hints tips and views. I’d recommend it to graduate students and others who are starting in the field of fibre scattering, and who are planning to do some beamline experiments.  

Hi all. I needed some time to get back on my feet after the HERCULES course. I’ll be posting updates soon! 

I’m at the HERCULES course at the moment, which is a five-week course at the ESRF (one week is spent at the Soleil synchrotron) on X-Ray and Neutron techniques. So far, my impressions are very positive. The lectures are excellent, the topics interesting, and there’s certainly a high information density there, with about 6 hours of lectures per day. There is also ample opportunity to meet fellow (”geek”) students, from a broad range of backgrounds working on a wide range of topics. They are by far the most well-behaved bunch of students in the lecture rooms I’ve seen so far…Thus far we’ve had introductory lectures about optics, detectors, crystallography, and more general aspects of X-Ray and neutrons. We’ve also been inside the ILL neutron reactor, as well as the ESRF. Over the next weeks, the more tailored programmes start and thus we’ll split up to follow different lectures going more in-depth into techniques, optics and the likes.  All in all, I’d recommend anyone who is able and interested, to sign up for this course.

Ok, so I’ve been on holiday and haven’t updated the site in a while. My apologies for that.. I’ve been looking at some presentations from other groups and other organisations, and I see some very inspiring stuff there. Here’s what I’ve stumbled across in general: The TED talks are a collection of talks on a broad range of topics that have to do with technology. The talks can provide a nice bit of background information on interesting stuff besides one’s thesis topic. One can find, for example, excellent presentations on The mind, The Cassini-Huygens mission, Electroshock therapy, The end of the world, and Copyright.   A good friend has posted about a new site that aims to provide video tutorials to some of the (often poorly documented with a limited UI) academic software out there: Screencasts for scientists. - November 15th, 2007I’ll post more individual videos as I come across them. Off course, SciVee, Youtube and Google Video cannot be absent from this list. B. 

This is my poster submission for the Nano.DTU’s Fifth NanoDay.  NanoDay 2007 B. 

I’ve been working on a presentation and a poster, and I was happy to stumble across this weblog: Presentation zen.

The weblog contains many hints and tips with respect to presentations and slide design. On top of that, it also evaluates some of the presentations (some scientific in nature, some not) that are available online. There are a few evaluations of the difference in keynote speeches of Steve Jobs and Bill Gates here and here, which are particularly enlightening.

It has certainly opened my eyes towards “cleaner” slide design, and thus I’m thinking of experimenting with empty slides and leaving titles off of slides altogether. As the site indicated, this focuses more of the audience’s attention on the presenter, so it certainly requires a strong footing and calming of nerves. I’m curious as to how it will go.

The expected date of release of the SAXSGUI data analysis software is Monday the 5th of November.

Hello all.

A quick link to a place I stumbled across yesterday. iTunes U. It’s a collaboration that’s been around for a while between (American) universities and Apple iTunes. The universities post some of their lectures online, for all to view, in a sort of “open university”-style.

This allows for public access to lecture series in both video and audio, on general topics such as physics, chemistry and art. Besides that, there’s also a considerable library of free music from those universities. You may think of Mozart as sung by a choir, but also singer/songwriters.

Do check it out, if only for the music (some of which is rather good). This collaboration exemplifies the belief that knowledge should be shared, a similar goal as what I hope to achieve with this weblog.