When dealing with pref. orientation (PO),
like with structure, it should make physical sense. For example if you have
needle-like crystals pref. orientation coefficient should be greater than 1
(not less as in your case) and PO axis should be aligned along needle. However, often
needles are "flat" than PO is better described with 2 axis one along needle
(>1) and one perpendicular to the flat plane of the needle with PO <1.
Look also at the structure the axes should be parallel or perpendicular to the
chains or layers of the
structure.
In the file *.pcr, the setting of
preferred orientation vector Pr1 Pr2 Pr3 is 0 0 1 and
Nor=1 for the selection of Modified March's function. Then the values
of parameters achieved are: Pref1=0.63353, Pref2=0.91337. The
FullProf manual says for the Debye-Scherrer geometry of most neutron
powder diffractometers the opposite holds compared to usual X-ray powder
diffractometers, therefore I think it may be needle-like. When Pr1 Pr2
Pr3 is 1 0 0 or 0 1
0 ,Pref1=1.52598 Pref2= 0.74387. (1.) It shows the
planes normal to these two directions are
flat?
> Like Rp,
Rwp, Chi2, RB are respectively from 3.96, 5.33, 2.68,
5.80
>
to 3.35, 4.42, 1.85, 3.07.
This should pass a test of
statistical significance.
I made a hypothesis testing. H0: It needs not PO
correction.
The model with PO correction:
G1=sum[wi(Yi-Yc,i)^2]=(n-p1)*chi2=715*1.85=1322.75.
The model
without PO correction:
G2=sum[wi(Yi-Yc,i)^2]=(n-p2)*chi2=717*2.68=1921.56,
Then the F distribution is:
F=[(G2-G1)/(p1-p2)]/[G1/(n-p1)]=[(1921.56-1322.75)/2]/1.85
=161.84
The corresponding p value is 0.0. Hence the H0 are
rejected.
(2.)The course above is true?
In the appendix of the paper(1965) written by Hamilton, it
says" Interpolation procedures for values of b and (n-m)
not
found in the tables are based on the fact that
interpolation in F maybe carried out on the reciprocals of the degree of
freedom." (3.) Who knows how to use interpolation to get F values not
listed in the F table? Or is there a free program which may calculate
it? Because in realities, the degree of freedom is always too
large.
In the file *.sum, the deviance D is calculated, for
the model with PO correction, it's 0.134E+04 and
Dev*=1.880;
for the model without PO correction, it's
0.200E+04 and Dev*=2.785. (4.) What's the relations between the
deviance D and sum[wi(Yi-Yc,i)^2] ,Dev* and chi2? I think they
should have been the same. I've checked the paper(1990) by
Antoniadis, how the _expression_ now described in the
FullProf manual is deduced from the 2{ln(y,y)-ln(eta)}?
(5.) The model having anisotropic temperature
factors and the one just having isotropic temperature factors are nested? If
making a test with F distribution, usually how large the alfa
value is taken? 0.05 too?
Thanks in advance!
