Nic,
Thanks,it will take a while (as usual) to implement.
Bob
R.B. Von Dreele
IPNS Division
Argonne National Laboratory
Argonne, IL 60439-4814
-Original Message-
From: Nicolae Popa [mailto:[EMAIL PROTECTED]
Sent: Sunday, April 17, 2005 1:27 AM
To: rietveld_l@ill.fr
Bob,
A "nice" ma
Title: Message
Alan,
But the analytical representation of the profile,
even by empirical functions, also helps in the analysis of Size/Strain you don't
think?
You don't agree with 3 Lorentzians even if they are
sharper than two pVs?
Probably is a reason that I don't see.
Concerning the num
Buna Mateo (where from you know Romanian?),
I spiked about the "regular" Rietveld programs that operate in the space of
measurement.
Sure, FFT is a solution, but I'm not sure that is the best solution. Even
fast, the calculation of the profile by Fourier transform is longer than to
calculate by el
ROTECTED] Sent: Monday, April 18, 2005 3:33
PMTo: rietveld_l@ill.frSubject: Re: Size Strain in
GSAS
Alen,
you right, as far as the profile
corresponding to a given distribution is accurately described, any
representation is good. Nevertheless, at comparative accuracies, it is not
b
Title: Message
Alen,
you right, as far as the profile
corresponding to a given distribution is accurately described, any
representation is good. Nevertheless, at comparative accuracies, it is not
better to use a representation with smaller numbers of parameters?
The profile parameters are fu
>For the purists, just redo the calculation starting from different
points
>and you can evaluate the error in the distribution using a
>MonteCarlo-like approach...
Leonie,
Your error estimation procedure sounds a lot like the "boot strap"
method which I think has now gained credibility, see:
h
buna Nicolae,
> Not only arithmetic, I think is clear that both and c were refined in a
> whole pattern least square fitting. A private program, not a popular
> Rietveld program because no one has inplemented the size profile caused by
> the lognormal distribution.
not sure no one did.. we're wo
HI All,
It has been shown that when incorporating a priori information, Bayesian
approach is the logically the most consistent (Cox 1946), since it conserves
the probabilities and all information (Jaynes 2004). Least squares is a special
and limited case of Bayesian applications. There are many
hat a gaussian
Nicolae. Maybe there's no need for a pseuod-Voigt / Lorentzian
based approximations after all.
all
the best
Alan
-Original Message-From: Nicolae Popa
[mailto:[EMAIL PROTECTED] Sent: Sunday, April 17, 2005 9:00
AMTo: rietveld_l@ill.frSubject: Re: Size S
Ok, to exclude further speculations around Dv and Da and to close our
discussion I will rewrite those equations in terms of integral
breadths:
= 0.5/Beta + 0.25(2BetaL*Beta)^-0.5
sigma = (BetaL/Beta - 1/4)
where Beta and BetaL are the total and Lorentzian integral breadths of
TCH pV fitted to
Leonid,
The lognormal distribution for particle size is not my modeling
(unfortunately), but if you insist, let see once again your equations.
= Da + 0.25(DaDv)^0.5 and sigma = (Dv/Da - 1/2)/2
For lognormal distribution first equation becomes:
2=(4/3)(1+c)**2+(1/4)sqrt[2*(1+c)**5]
For c=0.05 we
Dear Nicolae,
I will comment only upon your last statement because the limitations of
your modeling are clear.
> Well, I don't know where from you taken these formulae
> but I observe that for spheres of equal radius, then zero dispersion,
> you have:
> sigma(D)=5/4, different from zero!
First
Dear Leonid,
See coments below.
>
> Dear Nicolae,
>
> This arithmetic is clear, thanks, but since you did not specify this
> exact way of calculation in the paper it was not evident. There are
> several other ways of deriving , for instance: to calculate Dv from
> the inverse integral breadth a
Bob,
A "nice" math. description amenable to RR exists, take a look at JAC(2002)
35, 338-346.
"Nice" because the size profile is described by a pV (at "regular" lognormal
dispersions) or by a sum of maximum three Lorentzians (at large lognormal
dispersions - those 3% that Alan spiked about). The b
Title: Message
Alan,
(i) but a sum of two Lorentzians is not sharper
than the sum of two pVs (Voigts)?
(ii) We fitted the exact size profile caused
by the lognormal distribution by a pV (for low lognormal dispersion) or by a sum
of maximum 3 Lorenzians (for large lognormal dispersion).
T
> Indeed you missed something. I presume you have the paper.
> Then, take a look to the formula (15a). This is the size
> profile for lognormal.
> There is the function PHI - bar of argument 2*pi*s*.
> Replace this function PHI - bar from (15a) by the _expression
> (21a) with the argument x=2*pi*s
From: Nicolae Popa [mailto:[EMAIL PROTECTED]
Sent: Thursday, April 14, 2005 9:11 AM
To: rietveld_l@ill.fr
Subject: Re: Size Strain in GSAS
Dear B
-Original Message-
From: Nicolae Popa [mailto:[EMAIL PROTECTED]
Sent: Thursday, April 14, 2005 9:11 AM
To: rietveld_l@ill.fr
Subject: Re: Size Strain in GSAS
Dear Bob,
would be time to
concentrate on strain, micro strain, surface roughness and then
disloactions
all the best
alan
-Original Message-
From: Nicolae Popa
[mailto:[EMAIL PROTECTED]]
Sent: Friday, April 15, 2005 9:30 AM
To: rietveld_l@ill.fr
Subject: Re: Size Strain in GSAS
Dear Bob,
Perhaps
ril 15, 2005 9:30
AMTo: rietveld_l@ill.frSubject: Re: Size Strain in
GSAS
Dear Bob,
Perhaps I was not enough clear. Let me be more
explicit.
It's about one sample of CeO2 (not that from
round-robin) that we fitted in 4 ways.
(i) by GSAS with
TCH-pV
(ii) by
PROTECTED] Sent: Thursday, April 14, 2005 9:11
AMTo: rietveld_l@ill.frSubject: Re: Size Strain in
GSAS
Dear Bob,
If I understand well, you say that eta>1
(super Lorenzian) appeared only because eta was free parameter, but if TCH
is used super Loreanzians do not
rgonne, IL 60439-4814
-Original Message-From: Nicolae Popa
[mailto:[EMAIL PROTECTED] Sent: Thursday, April 14, 2005 9:11
AMTo: rietveld_l@ill.frSubject: Re: Size Strain in
GSAS
Dear Bob,
If I understand well, you say that eta>1
(super Lorenzian) appeared only because eta was fr
hursday, April 14, 2005 8:10
AMTo: rietveld_l@ill.frSubject: Re: Size Strain in
GSAS
Right, is rare, but we have meet once. A cerium
oxide sample from a commercial company, c=2.8. I don't know if they did
deliberately, probably not, otherwise the hard work to o
gonne, IL 60439-4814
-Original Message-From: Nicolae Popa
[mailto:[EMAIL PROTECTED] Sent: Thursday, April 14, 2005 8:10
AMTo: rietveld_l@ill.frSubject: Re: Size Strain in
GSAS
Right, is rare, but we have meet once. A cerium
oxide sample from a commercial company, c=2.8. I do
D] Sent: Thursday, April 14, 2005 7:14
AMTo: [EMAIL PROTECTED]Cc:
rietveld_l@ill.frSubject: Re: Size Strain in
GSAS
>Dear Nicolae, >Maybe ya ploho chitayu i
ploho soobrazhayu, but even after your>explanation I can't see a way
to calculate from the results
Hi all,
Well, I thought I'd weigh in on this with a discussion of an aforementioned
SRM project:
We are in the final stages of preparing an SRM for determination of
crystallite size from line profile analysis. Through the course of his PhD
work and NIST postdoctoral position, Nick Armstrong ha
[mailto:[EMAIL PROTECTED] Sent: Thursday, April 14, 2005 7:14
AMTo: [EMAIL PROTECTED]Cc:
rietveld_l@ill.frSubject: Re: Size Strain in
GSAS
>Dear Nicolae, >Maybe ya ploho chitayu i
ploho soobrazhayu, but even after your>explanation I can't see a way to
calculate from the
>Dear Nicolae, >Maybe ya ploho chitayu i
ploho soobrazhayu, but even after your>explanation I can't see a way to
calculate from the results of>fitting described in chapters 6
& 7 of JAC 35 (2002) 338-346. From such>fitting you obtain only
dispersion parameter c. Or I missed something?>Anywa
> It is not exact what you say, ty ploho cital.
> 6 & 7 from JAC 35 (2002) 338-346 gives the size profile - formulae
> (15a)
> combined with (21,22)
> or (20a) combined with (23,24). If you look carefully, these profiles
> are
> approximated by pseudo-Voigt or sums of 2 or 3 Lorentzians. These
>
...
>
> Yes, profiles can be approximated, but the question is not in
> approximating profiles. The primary topic of the discussion is "Size
> Strain in GSAS". GSAS and most other Rietveld refinement programs use
> TCH-pV profile function which provides the simplest and m
s can sometimes be long
> adventures...
Yes, profiles can be approximated, but the question is not in
approximating profiles. The primary topic of the discussion is "Size
Strain in GSAS". GSAS and most other Rietveld refinement programs use
TCH-pV profile function which provides the si
adventures...
Davor
> -Original Message-
> From: Leonid Solovyov [mailto:[EMAIL PROTECTED]
> Sent: Wednesday, April 13, 2005 12:11 AM
> To: rietveld_l@ill.fr
> Subject: Re: Size Strain in GSAS
>
> > 8. The simple modified TCH model ("triple-Voigt"), used in
> 8. The simple modified TCH model ("triple-Voigt"), used in most major
> Rietveld programs these days, is surprisingly flexible. It works well
> for most of the samples ("super-Lorentzian" is an example when it
> fails, as well as many others, but this is less frequent that
> onewould expect) and
; calculation includes many approximations of different kinds. There were
> numerous examples in literature showing that a simple Voigt function was
> able to approximate quite different cases. Of course, that is not true in
> general.
>
>
>> -Original Message-
>> F
rent kinds. There were numerous examples
in literature showing that a simple Voigt function was able to approximate
quite different cases. Of course, that is not true in general.
> -Original Message-
> From: Matteo Leoni [mailto:[EMAIL PROTECTED]
> Sent: Tuesday, March 29, 2005
Hi,
Long text but not fully convincing. At least concerning my questions (still
posted at the bottom). I'm risking a hurry reply without reading all
references (including "to be published" and PhD Thesis).
See comments below.
> that likelihood term is described by a goodness of fit, say chi-squar
Dear All,
I'm sorry for the delay in relying. I also want to pass on my thanks to
Jim Cline for pointing out that wasn't around to response to some of the
queries/issues. It has been interesting reading the discussion, since
coming back to Sydney. I don't mean to add more fuel to the fire, but I
Dear Matteo,
Thanks for the problem.
I have used pseudo voigt function to fit the peaks and finally used the program
BREADTH and obtained Dv=31 A, Da=18 A.
Please send me your simulation parameters, plots/calculations.
Regards,
Apu
/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
Apu Sarkar
Res
Dear Matteo,
Thanks for the exercise.
>From pseudo-Voight fitting I have got Dv=33A, Da=23A,
which gives the average size =21A and the relative
dispersion c=0.28 (c = [sigma/]^2).
However, I suspect that the actual values you used for the simulation
were ~30A and c~0.25.
Do I win the F1 GP? :-)
Leonid,
> Could you, please, give a reference to a study where Dv and Da sizes
> were derived from the parameters of pseudo-Voight or Voight fitted to
> simulated profiles for various size distribution dispersions?
I did something better (I hope).. at the end of the mesg you find xy
data with a
>done several times...
>
>With a whole pattern approach and working directly with the profile
>arising from a distribution of domains, in most cases you're able to
>recostruct the original distribution without making any assumption on
>its functional shape (after all, most of the information to
Leonid (and others)
just my 2 cents to the whole story (as this is a long standing point of
discussion: Davor correct me if I'm wrong, but this was also one of the
key points in the latest size-strain meeting in Prague, right?)
> Your recipe for estimating size distribution from the parameters
Hi,
Nick Armstrong has advised me he will in non-email-land for a week or so.
I'm sure he'll resume this discussion when he returns...
Jim
At 03:45 PM 3/28/2005 +0400, you wrote:
Hi,
So, to resume your statements, by using Bayesian/Max.Entr. we can
distinguish between two distributions that can not
3-871-4405
Web: www.du.edu/~balzar
> -Original Message-
> From: Leonid Solovyov [mailto:[EMAIL PROTECTED]
> Sent: Sunday, March 27, 2005 12:49 AM
> To: rietveld_l@ill.fr
> Subject: RE: Size Strain In GSAS
>
> On Friday 03/25 Davor Bal
gt; Sent: Sunday, March 27, 2005 12:49 AM
> To: rietveld_l@ill.fr
> Subject: RE: Size Strain In GSAS
>
> On Friday 03/25 Davor Balzar wrote:
> > Paragraph 3.3 of the article that you mentioned explains how were
> >size and strain values calculated. One can even obtain si
Hi,
So, to resume your statements, by using Bayesian/Max.Entr. we can
distinguish between two distributions that can not be distinguished by
maximum likelihood (least square)? Hard to swallow, once the restored peak
profiles are "the same" inside the noise. What other information than the
peak pro
On Friday 03/25 Davor Balzar wrote:
> Paragraph 3.3 of the article that you mentioned explains how were
>size and strain values calculated. One can even obtain size
> distribution by following the procedure that was posted to this
> mailing list several months ago;
Dear Davor,
Your recipe for
Hi
Sorry for the delay. The Bayesian results showed that the lognormal was more
probable. Yes, the problem is ill-condition which why you need to use the
Bayesian/Maximum entropy method. This method takes into account the
ill-conditioning of the problem. The idea being it determines the most pro
Hi, once again,
Fine, I'm sure you did. And what is the most plausible, lognormal or gamma?
>From the tests specific for least square (pattern fitting) they are equally
plausible. And take a combination of the type w*Log+(1-w)*Gam, that will be
equally plausible.
On the other hand, why should beli
Hi,
I pointed out that each model needs to be tested and their plausibility
determined. This can be achieved by employing Bayesian analysis, which takes
into account the diffraction data and underlying physics.
I have carried out exactly same analysis for the round robin CeO2 sample for
both
Hi,
But the diffraction alone cannot determine uniquely the physical model. An
example at hand: the CeO2 pattern from round-robin can be equally well
described by two different size distributions, lognormal and gamma and by
any linear combinations of these two distributions. Is the situation
diff
al or other assumed
> > distribution is one POSSIBLE approximation of the real size
> > distribution in
> > the sample. However, this equally applies to all the other
> parameters> obtained through the Rietveld refinement and is not a
> special
> > deficiency of
&
icult to
> discern between different bell-shaped size distributions,
> especially if the
> size distribution is narrow.
>
> Davor
> -Original Message-
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]
> Sent: Friday, March 25, 2005 4:01 AM
> To: rietveld_l@ill
Hi,
I wrote an article [ that appeared in Dean Smith's book ] some time back
that describes how to use SRM 660a, LaB6, and the TCH function of GSAS for
characterization of the IPF, and then refine the only the microstructure
specific terms for an estimation of the "size" and "strain" in subseque
Dear Apu,
difficult to say without seeing the pattern with your actual fitting.
Broadening with small domain size is normally more easy to fit. It
could be you didn't use the proper function or refines all necessary
parameters, or there is an anisotropic broadening or faulting.
Every sample/anal
Dear Andreas,
I didn't said "it cannot be done". Only that "was not made for" and so
it is not easy as using other tools. In principle every diffraction
fitting program can be used for size-strain.
Few questions: have you ever tried to do such analysis with GSAS the
right way using the instrumen
Dear all,
I think the statement that one cannot do line-profile analysis using GSAS is
too strong. In principle it is possible to do some
size strain analysis using GSAS, if the instrumental profile is e.g.
sufficiently described previously
by the Thompson-Cox-Hastings (TCH) profile function
Dear Prof. Lutterotti,
I was also aware of the fact that GSAS is not made for Size Strain analysis. I
got interested to use the Size strain refinement feature of GSAS only after
going through the article :
"Size-strain line broadening analysis of the ceria round-robin sample" by Prof.
D. Balzar
Dear Apu,
I know I will start up a "good" debate here, but size-strain analysis
with GSAS is a non-sense. The program was not written with that purpose
in mind and in fact it does not contains the instrumental aberration
part of the broadening that is necessary for such computation.
Indeed it is
Dear All, I am trying to perform Rietveld refinement on a very simple system using GSAS. I have obtained a reasonable fit except the peak widths. I want to use the size and strain refinement option in GSAS to make the fit well. Please tell me how to use the SIZE STRAIN refinement option in GSAS. P
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