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> I believe he means something that is relevant to real life where > crystals are small, diffraction weak, and background high, i.e. a > quantity that can realistically be extracted from the crap we get on our > images. Frank, my point was that in the presence of DS (which for protein crystals mean always), it's actually impossible to extract the Bragg component from the images without assuming some kind of model for the DS, i.e. anywhere in the spectrum between the simplistic 'tails' method (which is of course empirical and approximate), to a full-blown dynamical model. I believe pretty well everyone agrees that I(Bragg) is defined as the component of the diffraction arising from the average density, and we don't need to define it any other way. Note that I'm *not* saying that *none* of the DS can be modelled by a planar background: only the 'optic' & 'acoustic' contributions are sufficiently non-uniform that a planar background model won't remove them. The other main contribution, named after A. Einstein after his model of a solid as a lattice of independent quantum harmonic oscillators, and which arises from correlated displacements of electrons attached to atoms whose mean displacements are uncorrelated relative to all the other atoms, is sufficiently locally uniform that it can be modelled by a planar background, and therefore the integrated intensity obtained consists only of I(Bragg) + I(DSacoustic) + I(DSoptic). Cheers -- Ian Disclaimer This communication is confidential and may contain privileged information intended solely for the named addressee(s). It may not be used or disclosed except for the purpose for which it has been sent. If you are not the intended recipient you must not review, use, disclose, copy, distribute or take any action in reliance upon it. If you have received this communication in error, please notify Astex Therapeutics Ltd by emailing [log in to unmask] and destroy all copies of the message and any attached documents. Astex Therapeutics Ltd monitors, controls and protects all its messaging traffic in compliance with its corporate email policy. The Company accepts no liability or responsibility for any onward transmission or use of emails and attachments having left the Astex Therapeutics domain. Unless expressly stated, opinions in this message are those of the individual sender and not of Astex Therapeutics Ltd. The recipient should check this email and any attachments for the presence of computer viruses. Astex Therapeutics Ltd accepts no liability for damage caused by any virus transmitted by this email. E-mail is susceptible to data corruption, interception, unauthorized amendment, and tampering, Astex Therapeutics Ltd only send and receive e-mails on the basis that the Company is not liable for any such alteration or any consequences thereof. Astex Therapeutics Ltd., Registered in England at 436 Cambridge Science Park, Cambridge CB4 0QA under number 3751674