Yes it does look an like Airy disk but I can't see how it can be. 1. Airy disks are produced by a source (e.g. a star or an x-ray source) coherently illuminating an object (e.g. a telescope aperture, a round microcrystal). I would not have thought the coherence of the lab based source would be sufficient to do this (but see 2. below). If it was, one would in any case see interference effects between the microcrystals. For an example of coherent illumination of (inorganic) microcrystals and domains see J Synchrotron Radiat. 2010 Nov;17(6):751-60.
2. If they were Airy disks, the diameter for the first subsidiary maxima would be the same as the distance between the principal spots. This seems to be too much of a coincidence and would imply the size of the microcrystal is similar to the size of the unit cell. 3. The central spots are too sharp to be Airy disks. Having said that, the explanation I gave is not ideal. The extra spots are more diffuse than the main ones and don't all appear to be half way between the principal ones. A more detailed examination of the extra spots (I do think they are spots) is required. Regards Colin > -----Original Message----- > From: Jacob Keller [mailto:j-kell...@fsm.northwestern.edu] > Sent: 04 November 2010 00:57 > To: Nave, Colin (DLSLtd,RAL,DIA); CCP4BB@JISCMAIL.AC.UK > Subject: Re: [ccp4bb] Strange spots > > I don't think it looks like satellite spots at all--it looks > more like a flat diffuse scattering background or perhaps a > diffuse ring, with some strange blanking/clearing of a circle > around the spot. Perhaps it is a result of having not just > the usual convolution of the molecule with the lattice, but > an added level of a small number (say tens to hundreds) of > similar microcrystals within the crystal, whose diffraction > is also part of the convolution, but whose small number > results in broadening of the spots, making Airy disks? Look > at the attached image for what I found on wiki diffraction > (http://en.wikipedia.org/wiki/Diffraction): Airy disks around > stars, which look pretty exactly like our diffraction spots. > Same phenomenon? The caption for the image is "The Airy disk > around each of the stars from the 2.56 m telescope aperture > can be seen in this lucky image of the binary star zeta > Boötis." I have not convinced myself, however, that the small > number of crystals (my suggestion) could make Airy disks. > Maybe the pin, or something else, got in the way? > > JPK > > > ----- Original Message ----- > From: "Colin Nave" <colin.n...@diamond.ac.uk> > To: <CCP4BB@JISCMAIL.AC.UK> > Sent: Wednesday, November 03, 2010 12:52 PM > Subject: Re: [ccp4bb] Strange spots > > > OK! John prompted me to look more carefully at the images and they > don't seem to be consistent with any optics or detector effect. > > Attached a Blowup (almost as strange as Antonioni's 1966 film > with this > name) of one of the areas. As others have pointed out already, the > features are not round halos surrounding the spots though > they look like > this at first glance. They seem to consist of fuzzier > subsidiary spots. > If these spots were oriented in a 6 fold manner, this would, > I think be > consistent with a commensurate modulation with q=0.5a* (assuming the > subsidiary spots are half way between the main spots). However, there > seems to be some evidence that the subsidiary spots around each main > spot are 30 degrees apart not 60 degrees. A bit difficult to see > though. Looking at the movie, I think they are most visible for zones > with constant l (h and k varying) though they presumably occur > elsewhere. I presume the indexing would reveal this. It might be worth > trying to index on a supercell with a=146A and see if there > is anything > left. > > Regards > Colin > > > > > > > -----Original Message----- > > From: CCP4 bulletin board [mailto:ccp...@jiscmail.ac.uk] On > > Behalf Of John R Helliwell > > Sent: 03 November 2010 17:00 > > To: CCP4BB@JISCMAIL.AC.UK > > Subject: Re: [ccp4bb] Strange spots > > > > Dear David, > > Many thanks indeed for this movie and the extra info. > > It is quite captivating! > > > > The 'strange spot' features do seem progress to other regions > > of reciprocal space at approximately constant diffraction > > resolution in an anti-clockwise manner.....but I am still > > digesting your movie.... > > > > Behind the scenes discussion, between Colin Nave, James > > Holton and myself, has been going on. Since Colin has been > > the main leader in these I leave it to Colin to take it up > > from here and I can chip in if I can add anything. > > > > Greetings, > > John > > > > On Wed, Nov 3, 2010 at 3:53 PM, David Goldstone > > <david.goldst...@nimr.mrc.ac.uk> wrote: > > > Dear All, > > > > > > Thank you for the replies sorry about the delay in my > > reply. Here is > > > some more information, for those of you that are > interested, to try > > > fill in some gaps. > > > > > > The data was collected on our home source with osmic > > vairmax-HF optics > > > and an RAXISIV++ detector. We are investigating whether it is an > > > optics issue but this is unlikely as other crystals in the > > screening > > > run didn't display this phenomenon. > > > > > > The crystal was grown in the presence of 12% glycerol and > > transfered > > > to 20% glycerol as a cryo. I haven't tried other cryos as crystals > > > also grow in 20% glycerol and do not require further > cryoprotectant. > > > > > > I have uploaded a movie showing a wedge of data showing how the > > > circles around the spots progress. > > > http://www.4shared.com/video/o8_YmInD/Spot_defect.html (~12mb > > > download) > > > > > > The crystals index and scale in p6122 (a=b=73, c=110) > with a single > > > monomer in the ASU (by matthews, 45% solvent). We do however see a > > > peak in the native patterson at (0,0,0.2 ~50% origin height). > > > > > > Cheers > > > > > > Dave > > > > > > > > > On 29/10/2010 17:08, David Goldstone wrote: > > >> > > >> Dear All, > > >> > > >> Does anyone have any insight into what the circles around > > the spots > > >> might be? > > >> > > >> cheers > > >> > > >> Dave > > > > > > -- > > > David Goldstone, PhD > > > National Institute for Medical Research Molecular Structure The > > > Ridgeway Mill Hill London NW7 1AA > > > > > > > > > > > -- > > Professor John R Helliwell DSc > > > > > > ******************************************* > Jacob Pearson Keller > Northwestern University > Medical Scientist Training Program > Dallos Laboratory > F. Searle 1-240 > 2240 Campus Drive > Evanston IL 60208 > lab: 847.491.2438 > cel: 773.608.9185 > email: j-kell...@northwestern.edu > ******************************************* >
