Good morning Colin (from this side of the pond), I never liked the word redundancy. Multiplicity is a however a good word for multiple measurements. So, Ethan, what does someone in the USA say when made redundant ie out of a job? Surely not that they are now a useful surplus for the US economy of the future?
Re benefits of multiple measurements I would add:- Any time dependent related variations such as :- X-ray beam rapid variations; Crystal movements; Variations in cold stream flow; ?? ?? More esoterically perhaps extinction for very strong reflections in bigger crystal cases with longer Xray wavelengths. This would be data sets where multiple crystals are needed. This however I don't think affects more than a handful of reflections. Just my two UK pennies worth, John Prof John R Helliwell DSc On 14 May 2013, at 21:58, Colin Nave <[email protected]> wrote: > Yes, a good summary. > The use of the term redundancy (real or otherwise!) in crystallography is > potentially misleading as the normal usages means superfluous/ surplus to > requirements. The closest usage I can find from elsewhere is in information > theory where it is applied for purposes of error detection when communicating > over a noisy channel. Seems similar to the crystallographic use. > > The more relevant point is what sort of errors would be mitigated by having > different paths through the crystal. The obvious ones are absorption errors > and errors in detector calibration. Inverse beam methods can mitigate these > by ensuring the systematic errors are similar for the reflections being > compared. However, my interpretation of the Acta D59 paper is that it is > accepted that systematic errors are present and, by making multiple > measurements under different conditions, the effect of these systematic > errors will be minimised. > > Can anyone suggest other sources of error which would be mitigated by having > different paths through the crystal. I don't think radiation damage > (mentioned by several people) is one. > > Colin > > From: CCP4 bulletin board [mailto:[email protected]] On Behalf Of Frank > von Delft > Sent: 14 May 2013 14:23 > To: ccp4bb > Subject: [ccp4bb] Fwd: Re: [ccp4bb] reference for "true multiplicity"? > > George points out that the quote I referred to did not make it to the BB -- > here we go, read below and learn, it is a most succinct summary. > phx > > -------- Original Message -------- > Subject: > > Re: [ccp4bb] reference for "true multiplicity"? > > Date: > > Tue, 14 May 2013 09:25:22 +0100 > > From: > > Frank von Delft > <[email protected]><mailto:%[email protected]%3e> > > To: > > George Sheldrick > <[email protected]><mailto:[email protected]> > > > Thanks! It's the Acta D59 p688 I was thinking of - start of discussion: > "The results presented here show that it is possible to solve > protein structures using the anomalous scattering from native > S atoms measured on a laboratory instrument in a careful but > relatively routine manner, provided that a sufficiently high > real redundancy is obtained (ranging from 16 to 44 in these > experiments). Real redundancy implies measurement of > equivalent or identical re¯ections with different paths through > the crystal, not just repeated measurements; this is expedited > by high crystal symmetry and by the use of a three-circle (or ) > goniometer." > Wise words... > > phx > > > On 14/05/2013 08:06, George Sheldrick wrote: > Dear Frank, > > We did extensive testing of this approach at the beginning of this millenium > - see > Acta Cryst. D59 (2003) 393 and 688 - but never claimed that it was our idea. > > Best wishes, > George > > On 05/14/2013 06:50 AM, Frank von Delft wrote: > > Hi, I'm meant to know this but I'm blanking, so I'll crowdsource instead: > > Anybody know a (the) reference where it was showed that the best SAD data is > obtained by collecting multiple revolutions at different crystal offsets > (kappa settings)? It's axiomatic now (I hope!), but I remember seeing > someone actually show this. I thought Sheldrick early tweens, but PubMed is > not being useful. > > (Oh dear, this will unleash references from the 60s, won't it.) > > phx > > > > > > > -- > > This e-mail and any attachments may contain confidential, copyright and or > privileged material, and are for the use of the intended addressee only. If > you are not the intended addressee or an authorised recipient of the > addressee please notify us of receipt by returning the e-mail and do not use, > copy, retain, distribute or disclose the information in or attached to the > e-mail. > > Any opinions expressed within this e-mail are those of the individual and not > necessarily of Diamond Light Source Ltd. > > Diamond Light Source Ltd. cannot guarantee that this e-mail or any > attachments are free from viruses and we cannot accept liability for any > damage which you may sustain as a result of software viruses which may be > transmitted in or with the message. > > Diamond Light Source Limited (company no. 4375679). Registered in England and > Wales with its registered office at Diamond House, Harwell Science and > Innovation Campus, Didcot, Oxfordshire, OX11 0DE, United Kingdom > > > > > > > > >
