The question was: which is F+ and which F-.
I think the answer is that the hkl are in a right-handed axis system and
-h-k-l are in a left-handed one. So it's the guy who first decides which
are a,b,and c. I think his name is denzo.
BS
On Fri, 27 Jun 2008, James Holton wrote:
> Ahh. The history of science. I've always wondered how these naming
> conventions get decided. Who is the authority on what gets named after who?
> Historically, it seems to vary a lot.
>
> - When Patterson published his incredibly useful map he called it the
> "F-square synthesis". Does anyone NOT call it a Patterson map?
>
> - When Rontgen discovered a new kind of light, he called it "x-rays". Now
> only the Germans call them Rontgen rays.
>
> - When the largest protein ever was discovered, it was called "connectin",
> but a subsequent paper called it "titin" and the second name has stuck. I
> actually can't remember who the "connectin" guy was ...
>
> - When Joseph Fourier discovered that heat radiated from the earth could be
> reflected back by gasses in the atmosphere, he simply named it by describing
> it (in French). Now this is (incorrectly) called the "greenhouse effect".
> Why not the Fourier effect? Fortunately for Fourier, a mathematical series
> was named after him, although he neither discovered it (Budan did that), nor
> implemented it (Navier did that). All Fourier did was present a theorem
> based on a flawed premise that turned out to be right anyway.
>
> So, I decided to look up Friedel and Bijvoet in the Undisputed Source of All
> Human Knowledge (wikipedia) and found that Friedel's Law "... is a property
> of Fourier transforms <http://en.wikipedia.org/wiki/Fourier_transform> of
> real functions."
>
> I am willing to believe that. And considering this origin I would think it
> appropriate to call (hkl) and (-h-k-l) a "Friedel pair" (or "Friedel's pair"
> as it is described in the USAHK). G. Friedel was indeed a crystallographer,
> but I doubt he considered more than this simple centrosymmetric property.
> Who would care in 1913 which is F+ and F-? The atomic scattering factors had
> not yet been worked out at that time. Ewald may have predicted it, but
> anomalous scattering was not shown to exist until the classic work of Koster,
> Knol and Prins (1930). I guess that goes to show that if you want something
> named after you... keep it at one or two authors.
>
> Perhaps it has to do with the original paper getting old enough that it gets
> too hard to find. I'm sure in G. Friedel's paper in 1913 he cited Joseph
> Fourier's Paper from 1822. Or did he? I wonder if they were already calling
> it a Fourier Transform at that time?
>
> Okay, so what, exactly did Bijvoet do? Everyone cites his Nature paper
> (1951), but one thing that I was NOT KIDDING about in my April Fool's joke
> was that this paper (like so many other high-profile papers) contains almost
> no information about how to reproduce the results. I was also not kidding
> that boring little details like the reasoning behind the conclusion (the hand
> of the microworld) were relegated to a more obscure journal (the one in the
> Proc. Royal. Soc. Amsterdam). I WAS kidding about having found and read that
> paper. I have never seen it. Still, Bijvoet did the first experiment to
> elucidate the absolute configuration, and he definitely deserves credit for
> that.
> So, particularly in that light, I would agree that any pair of reflections
> that would be equivalent if not for anomalous scattering effects could be
> called a "Bijvoet pair". This is because they contain the information needed
> to apply Bijvoet's technique.
> Something that has always eluded me is who decided which is F+ and F-? After
> all, the reciprocal lattice is very very nearly centrosymmetric. You cannot
> tell by looking at a single diffraction image whether that spot at a given
> X,Y pixel coordinate is F+ or F-, you need to know the axis convention of the
> camera. At some point in writing the CCP4 libraries with their asymmetric
> unit definitions, someone must have established a convention. What is it?
> To me, the reasoning behind these assignments is, in fact, they key to
> assigning the absolute configuration, not the anomalous scattering effect
> itself. So, who worked this out? Should we really be calling them Dodson
> pairs?
>
> -James Holton
> MAD Scientist
>
--
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Robert M. Sweet E-Dress: [log in to unmask]
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Biology Dept
Brookhaven Nat'l Lab. Phones:
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