For the history buffs and crystallographers needing some R&R and chill-out, an interesting historic fiction read about the era of Newton and Leibnitz and the foundation of the Royal Society is the Baroque cycle by Neil Stevenson. http://en.wikipedia.org/wiki/The_Baroque_Cycle Cryptonomicon, although written before, picks up a descendent of a character from the Cycle, and can be considered imho the 4th book http://en.wikipedia.org/wiki/Cryptonomicon All together ~ 2400 pages. Cheap on Amazon 3rd party. Book a long vacation. Best, BR
-----Original Message----- From: CCP4 bulletin board [mailto:CCP4BB@JISCMAIL.AC.UK] On Behalf Of Ian Tickle Sent: Sunday, January 29, 2012 5:23 AM To: CCP4BB@JISCMAIL.AC.UK Subject: Re: [ccp4bb] MAD Hi Peter You are right: the location of the prism experiment is most likely the study at Woolsthorpe, e.g. see http://www.isaacnewton.org.uk/texts/OfColours7 . Newton was admitted to Trinity College in 1661 as a 'sizar' (a paid part-time student employed by the College) but was forced to return to Woolsthorpe (the family home) in August 1665 (http://www.isaacnewton.org.uk/Chronology) to continue studying privately, because the University closed temporarily as a precaution against the Great Plague ('Black Death') which was spreading outwards from the initial outbreak in this country in the London Docklands during the summer of that year. He returned to Trinity in 1667 as a Fellow of the College. So I should have been more precise and said that Newton performed the prism experiment during the time that he was associated with Trinity (it's not clear what the nature of his association with Trinity was during the 2 years he spent doing experiments at Woolsthorpe). Cheers -- Ian On 28 January 2012 09:35, Peter Moody <pcem1bigfi...@gmail.com> wrote: > Ian, > If you visit Isaac Newton's old home at Woolsthorpe (near here) you > will see a conflicting claim for location of the classic prism > experiment. You will also find an apple tree in the garden, but that is another story...... > > Peter > > PS this is my special ccp4bb email account, it doesn't always get the > attention it deserves. > > > On 19 January 2012 17:50, Ian Tickle <ianj...@gmail.com> wrote: >> >> Perhaps I could chime in with a bit of history as I understand it. >> >> The term 'dispersion' in optics, as everyone who knows their history >> is aware of, refers to the classic experiment by Sir Isaac Newton at >> Trinity College here in Cambridge where he observed white light being >> split up ('dispersed') into its component colours by a prism. This >> is of course due to the variation in refractive index of glass with >> wavelength, so then we arrive at the usual definition of optical >> dispersion as dn/dlambda, i.e. the first derivative of the refractive >> index with respect to the wavelength. >> >> Now the refractive index of an average crystal at around 1 Ang >> wavelength differs by about 1 part in a million from 1, however it >> can be determined by very careful and precise interferometric experiments. >> It's safe to say therefore that the dispersion of X-rays (anomalous >> or otherwise) has no measurable effect whatsoever as far as the >> average X-ray diffraction experiment (SAD, MAD or otherwise) is >> concerned. The question then is how did the term 'anomalous >> dispersion' get to be applied to X-ray diffraction? The answer is >> that it turns out that the equation ('Kramer-Kronig relationship') >> governing X-ray scattering is completely analogous to that governing >> optical dispersion, so it's legitimate to use the term 'dispersive' >> (meaning 'analogous to dispersion') for the real part of the >> wavelength-dependent component of the X-ray scattering factor, >> because the real part of the refractive index is what describes >> dispersion (the imaginary part in both cases describes absorption). >> >> So then from 'dispersive' to 'dispersion' to describe the wavelength >> dependence of X-ray scattering is only a short step, even though it >> only behaves _like_ dispersion in its dependence on wavelength. >> However having two different meanings for the same word can get >> confusing and clearly should be avoided if at all possible. >> >> So what does this have to do with the MAD acronym? I think it >> stemmed from a visit by Wayne Hendrickson to Birkbeck in London some >> time around 1990: he was invited by Tom Blundell to give a lecture on >> his MAD experiments. At that time Wayne called it multi-wavelength >> anomalous dispersion. Tom pointed out that this was really a >> misnomer for the reasons I've elucidated above. Wayne liked the MAD >> acronym and wanted to keep it so he needed a replacement term >> starting with D and diffraction was the obvious choice, and if you >> look at the literature from then on Wayne at least consistently >> called it multi-wavelength anomalous diffraction. >> >> Cheers >> >> -- Ian >> >> On 18 January 2012 18:23, Phil Jeffrey <pjeff...@princeton.edu> wrote: >> > Can I be dogmatic about this ? >> > >> > Multiwavelength anomalous diffraction from Hendrickson (1991) >> > Science Vol. >> > 254 no. 5028 pp. 51-58 >> > >> > Multiwavelength anomalous diffraction (MAD) from the CCP4 >> > proceedings >> > http://www.ccp4.ac.uk/courses/proceedings/1997/j_smith/main.html >> > >> > Multi-wavelength anomalous-diffraction (MAD) from Terwilliger Acta >> > Cryst. >> > (1994). D50, 11-16 >> > >> > etc. >> > >> > >> > I don't see where the problem lies: >> > >> > a SAD experiment is a single wavelength experiment where you are >> > using the anomalous/dispersive signals for phasing >> > >> > a MAD experiment is a multiple wavelength version of SAD. >> > Hopefully one picks an appropriate range of wavelengths for >> > whatever complex case one has. >> > >> > One can have SAD and MAD datasets that exploit anomalous/dispersive >> > signals from multiple difference sources. This after all is one of >> > the things that SHARP is particularly good at accommodating. >> > >> > If you're not using the anomalous/dispersive signals for phasing, >> > you're collecting native data. After all C,N,O,S etc all have a >> > small anomalous signal at all wavelengths, and metalloproteins >> > usually have even larger signals so the mere presence of a >> > theoretical d" difference does not make it a SAD dataset. ALL >> > datasets contain some anomalous/dispersive signals, most of the >> > time way down in the noise. >> > >> > Phil Jeffrey >> > Princeton >> > >> > >> > >> > On 1/18/12 12:48 PM, Francis E Reyes wrote: >> >> >> >> >> >> Using the terms 'MAD' and 'SAD' have always been confusing to me >> >> when considering more complex phasing cases. What happens if you >> >> have intrinsic Zn's, collect a 3wvl experiment and then derivatize >> >> it with SeMet or a heavy atom? Or the MAD+native scenario (SHARP) >> >> ? >> >> >> >> Instead of using MAD/SAD nomenclature I favor explicitly stating >> >> whether dispersive/anomalous/isomorphous differences (and what >> >> heavy atoms for each >> >> ) were used in phasing. Aren't analyzing the differences >> >> (independent of >> >> source) the important bit anyway? >> >> >> >> >> >> F >> >> >> >> >> >> --------------------------------------------- >> >> Francis E. Reyes M.Sc. >> >> 215 UCB >> >> University of Colorado at Boulder > >
