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umar khan

How do we find Abase?

Hello, I wish to know how the base excitation amplitude Abase can be calculated.

Secondly, in the VEDA comprehensive manual (Febuary 2, 2009), there is multiplication of root(1 + (QiOmegai)^-2) in eq. 33, however no such factor is present in the corresponding eq. 7 of the paper “Invited article: VEDA: A web -based virtual environment for dynamic atomic force microscopy”. Can you please tell me if the two equations are same without this factor?

Best regards, Umar Khan.

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    Daniel Kiracofe

    Hello and thank you for your interest in VEDA.

    For the first question, in the latest version of the manual (dated Apr 4, 2011), the calculation of Abase is given in equations 61 – 64. Note there are a few typos in this version which I will fix in the next version. In (61) both y should have overbar, in (62) we use uppercase Y but everywhere else lowercase y. I will fix these typos in next version. Hopefully these equations are clear, if not please let me know.

    Note that most users will never need to calculate Abase themselves. You typically enter the tip amplitude and VEDA calculates Abase for you. To see what value it has calculated, look at the Misc. Internal Parameters result after the calculation.

    For the second question, eq 7 in 2008 RSI paper applied to the version of VEDA published at that time. Equation 7 includes only inertial forces from the base motion, it does not include viscous forces from the base motion. Therefore, Eq 7 is a reasonable approximation for air or vacuum where Q > 100. For liquid environments where Q is between 1 and 6, eq 7 is not accurate. Therefore, in the newer versions of VEDA, we have modified the excitation force for base motion. The current version of the manual (dated Apr 4, 2011) reflects the tool that is currently published. This is why the equations are different.

    By the way, it seems you are very interested in the details of acoustic mode. We are currently preparing a new version of VEDA and an accompanying paper which details significantly more accurate calculations for acoustic excitation in liquids. If you are interested, we may be able to get you a pre-print of the manuscript.

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