Title: Message
Dear all,
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!
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Zhijian Fan                
E-mail: [EMAIL PROTECTED]                 
 
 

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