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BrukerApplications posted on Thu, Nov 4 2010 6:00 PM

Why is a default value of 85% assigned to the fit region of Deformation? The manual (p.28, PeakForce User Guide) says: “This parameter is used to reduce the effect of baseline noise.”

What I was originally interested is to know whether this parameter (Deformation Fit Region) would affect the DMT Modulus calculation. It appears that it doesn’t because the two quantities (Deformation and DMT Modulus) are calculated independently on two sets of data and parameters. I understand that for the three “fit region” parameters (Top Fit Region, Deformation Fit Region and Unload Fit Region), Deformation Fit Region affects the Deformation value whilst Top Fit Region and Unload Fit Region affect the DMT Modulus value. In addition, the Deformation uses the loading curve, which includes both elastic and plastic deformation, whilst Modulus uses the unloading curve, which contains elastic deformation only.

It might be useful if the software could allow the user to use one of the eight data channels to record also the “unloading deformation” (or, equivalently, difference between the loading and unloading deformation) so that we could obtain both elastic and plastic deformation maps simultaneously.

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The specific situation that caused us to choose 85% is the sort of long range repulsion or baseline error shown in this curve:

This kind of thing is fairly common in fluid (double layer forces).  It is a little strange to call it noise, but it is not part of the sample deformation either.  If your curves look more normal and you have a jump to contact, you can use 100% and it should not be a problem.

Your comments in your second paragraph below are exactly right.  You can try adjusting the parms to see how much effect they have on the calculation.  I think you will see that there isn't much change as long as you have enough data points.

That is a good suggestion about the unloading deformation.  I'll see what I can do!

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