From: Walter Stafford <STAFFORD@bbri.org>
  To  : rasmb@bbri.org
  Date: Wed, 2 Jun 1999 9:33:45 -0400 (EDT)

re: radial step intervals in the XL scanning abs optics

Hi Arthur,

	This variation in radial step size seems to be a fact of life with the
absorbance optical scanning system. The front end of DCDT does an 
interpolation of each scan onto an equi-spaced radial grid and allows you to
rewrite the data in XL-I format (Macintosh PPC version) or in multi-column 
format (Mac and PC versions). 

Walter Stafford
===========================================================================
From:	SMTP%"arthur.rowe@nottingham.ac.uk"  2-JUN-1999 07:24:11.98
Subj:	radial step intervals in the XL scanning abs optics

Hi RASMBers !

Trying to do a bit of hard-nosed analysis of data from scanning absorption
optics, and wanting to have data equi-spaced in r (well - thats nice for all
sorts of good, sound, numerico-analytical reasons) I was struck by how
variable the step size in r seemed to be within a given run. 

With a nominal set interval of 2 micrometres, for a data set quite typica of
many, I found the following: 

=============================================
STATISTICS FOR FIRST DIFFERENCE IN r:

# Valid numbers       	=   	53
Sum                   	=   	0.1440
Mean                  	=   	2.7170e-3
Variance              	=   	2.1684e-6
Standard deviation    	=   	1.4725e-3
Mean abs. deviation   	=   	1.2374e-3
Skewness              	=   	0.5906
Kurtosis              	=  	-0.8024
Median                	=   	2.0003e-3
Maximum               	=   	6.0000e-3
Minimum               	=   	9.9993e-4
=============================================

In other words, the ACTUAL mean value was 2.72 micrometres, with a standard 
deviation of 1.47 micrometres, and individual values varying between 1 and 6 
micrometres !!!  Oddly enough, the MEDIAN value is almost precisely 2 
micrometres.

 I should say we have our XL-A regularly serviced, and the slit scanning
system was specifically checked (and its radial calibration) not long ago. 

What is the general experience here of XL users ?  Is this just one of those
things one has to put up with ? 

Best wishes to all 

Arthur Rowe 



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Professor Arthur J Rowe
NCMH Business Centre
University of Nottingham
School of Biological Sciences
Sutton Bonington
Leicestershire LE12 5RD   UK

phone/voicemail					+44 (0)115 951 6156
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